variable approaches investigating light quality and quantity impacts on warm
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Clemson UniversityTigerPrints
All Dissertations Dissertations
5-2008
VARIABLE APPROACHES INVESTIGATINGLIGHT QUALITY AND QUANTITYIMPACTS ON WARM- AND COOL-SEASONTURFGRASSESChristian BaldwinClemson University, torrey_christian@yahoo.com
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Recommended CitationBaldwin, Christian, "VARIABLE APPROACHES INVESTIGATING LIGHT QUALITY AND QUANTITY IMPACTS ONWARM- AND COOL-SEASON TURFGRASSES" (2008). All Dissertations. 201.https://tigerprints.clemson.edu/all_dissertations/201
i
VARIABLE APPROACHES INVESTIGATING LIGHT QUALITY AND
QUANTITY IMPACTS ON WARM- AND COOL-SEASON
TURFGRASSES
A Dissertation
Presented to
the Graduate School of
Clemson University
In Partial Fulfillment
of the Requirements for the Degree
Doctor of Philosophy
Plant and Environmental Sciences
by
Christian Michael Baldwin
May 2008
Accepted by:
Dr. Haibo Liu, Committee Chair
Dr. Lambert B. McCarty
Dr. Hong Luo
Dr. Joe E. Toler
ii
ABSTRACT
Bermudagrass (Cynodon spp.) is the most popular warm-season turfgrass used in
warm climatic regions of the world due its recuperative ability, high traffic tolerance,
heat tolerance, and relative drought and salt tolerance. However, shade is a
microenvironment in which bermudagrass performs poorly. Morphological limitations,
such as reduced lateral stem growth and overall reduction of carbohydrate synthesis
contribute to bermudagrass, a C4 plant, decline under shade. Therefore, primary
objectives of this dissertation were to determine the genetic diversity of bermudagrasses
grown in full-sunlight and shade, impacts of shade and cultural practices on
bermudagrass spring transition, management recommendations to enhance bermudagrass
putting greens under shade, and the impact of different types of light on warm-season
turfgrasses. Secondary objectives of this dissertation determined winter shade and traffic
impacts on creeping bentgrass putting greens.
Due to the genetic variability and shade sensitivity of bermudagrasses, a two-year
replicated field and greenhouse study determined the morphological and physiological
characteristics and relative shade tolerance of 42 bermudagrass cultivars selected from
the 2002 National Turfgrass Evaluation Program (NTEP). In the field study, few trends
emerged where one cultivar could be recommended above all others. Also, experimental
cultivars performed well compared to industry standards throughout the year. For
example, „OKC 70-18‟ and „SWI-1046‟ (spring), „TiftNo.2‟ (summer), and „SWI-1003‟,
„SWI-1044‟, „SWI-1045‟, „SWI-1001‟, „TiftNo.4‟, „Tifway‟, and „TiftNo.2‟ (fall), were
in the top statistical category for turfgrass quality (TQ), shoot chlorophyll, clipping yield,
iii
root biomass, and thatch. In the greenhouse study, cultivars with best shade tolerance
were „Celebration‟, TiftNo.4, „TiftNo.1‟, and „Transcontinental‟. Cultivars with
intermediate shade tolerance included „Aussie Green‟, „MS-Choice‟, „Princess 77‟, „SWI-
1045‟, „SWI-1041‟, and „SWI-1012‟. Most shade sensitive cultivars included „SWI-
1014‟, „Arizona Common‟, „Sundevil‟, „SR 9554‟, „GN-1‟, and „Patriot‟. Greenhouse
results indicate genetic variability of shade tolerance exists among bermudagrasses, while
future bermudagrass improvement focusing on shade tolerance is promising.
Two lysimeter studies were conducted from March to July 2006 and 2007 to
evaluate fairway-type bermudagrass cultivars spring green-up (SGU) when shade is a
growth limiting factor and to evaluate the impacts of different cultural practices
(overseed, colorant use, and dormant turfgrass) and shade on „TifEagle‟ bermudagrass
(Cynodon dactylon (L.) Pers. X C. transvaalensis Burtt-Davy) spring transition and
summer performance. Fairway-type cultivars, Celebration and TiftNo.4, did not show
significant SGU delays due to shade in year II. However, Yukon and Riviera delayed
SGU 11% and 50% compared to full-sunlight treatments on 9 May 2007. Compared to
full-sunlight, TiftNo.4 and Celebration SGU and summer TQ was least affected by shade.
Although cultivar summer TQ differences were noted when grown under shade, all
cultivars TQ was below the acceptable threshold of 7 by 31 July. In another lysimeter
study, shade negatively impacted TifEagle bermudagrass SGU for all treatments on
various rating dates. By the end of May, overseed sun treatment had 39% greater SGU
compared to overseed shade treatment. Shade-grown colorant-treated TifEagle showed
~37% SGU reduction from week 2 through week 5 ratings compared to sun-grown
iv
colorant treatment. On the final SGU rating date, sun-grown colorant treatment enhanced
SGU 39% compared to sun-grown overseed treatment. This study indicates colorant-use
may provide an alternative to overseeding for bermudagrass by providing adequate
winter color at certain sites and a stronger bermudagrass base compared to overseeding.
A two-year field study from 15 June to 15 September 2006 and 2007 at Clemson
University determined the best combination of management practices for sustaining a
high quality „Champion‟ bermudagrass putting green under shade. Treatments included
55% full-day shade, trinexapac-ethyl (TE) applications (0.05 kg a.i. ha-1
2wk-1
), iron (Fe)
applications (2.7 kg a.i. ha-1
2wk-1
), and nitrogen (N) applications as urea (46-0-0) at rates
of 147, 293, and 437 kg ha-1
yr-1
. Overall, Fe applications had minimal impacts on
parameters measured. Increasing N rates linearly increased TQ when grown under full-
sunlight. However, increasing N rates linearly decreased TQ scores under 55% full-day
shade. Applying TE resulted in a linear TQ increase for full-sunlight and shade-grown
Champion bermudagrass. A 15% chlorophyll concentration increase was noted for TE-
treated plots compared to non TE-treated plots when grown under shade. Applying N at
293 kg ha-1
yr-1
increased thatch thickness 26% compared to the 147 kg ha-1
yr-1
N rate.
Champion bermudagrass did not provide an acceptable quality putting green when grown
under 55% full-day shade, however, adjusting chemical and cultural management
practices improved Champion bermudagrass putting green when grown under shade.
In 2007, two repeated greenhouse research projects were initiated to investigate
the physiological and morphological responses of „Diamond‟ zoysiagrass (Zoysia
matrella (L.) Merr), „Sea Isle 2000‟ (Paspalum vaginatum Sw.) seashore paspalum,
v
Tifway bermudagrass, and Celebration bermudagrass to various light spectral qualities.
Light treatments included a full-sunlight control and four different color shade cloths
filtering wavelengths 560 - 720 nm (blue shade cloth), 360 – 520 nm (yellow shade
cloth), 360 - 560 nm (red shade cloth) and 360-720nm (black shade cloth). Red to far red
ratio for each cloth was ~1.171, while percent light reduction for each cloth was ~65%.
Data collection included visual TQ, clipping yield, total shoot chlorophyll, leaf width,
total root biomass, root length density (RLD), specific root length (SRL), and root and
shoot total non-structural carbohydrates (TNC). Overall, black shade most negatively
inhibited parameters measured followed by blue shade, while yellow and red shade
performed similarly. For turfgrasses, Diamond was the most shade-tolerant, while
Tifway was the most shade-sensitive. Celebration and Sea Isle 2000 performed similarly.
This study implies different types of shade significantly impact the performance of warm-
season turfgrasses.
Two replicated field studies were conducted to evaluate winter shade tolerance
under various reduced light environments and winter traffic tolerance of „L93‟ creeping
bentgrass (Agrostis stolonifera var. palustris (Huds.)). In the first field study, objectives
were to evaluate winter shade tolerance of „L93‟ creeping bentgrass under various
reduced light environments (55% and 95%), including effects of morning vs. afternoon
shade, effect of trinexapac-ethyl (TE) (4-(cyclopropyl- -hydroxy-methylene)-3,5-dioxy-
cyclohexanecarboxylic acid ethyl ester) application on shade tolerance, and summer
month performance following a winter shade environment. Under shade stress,
consistent TE applications every two weeks during winter negatively impacted bentgrass
vi
growth and color, however, TE enhanced spring recovery from 95% winter shade
damage. Morning or afternoon shade minimally impacted parameters measured.
Overall, moderate to heavy winter shade may not limit creeping bentgrass performance as
a putting green in the transition zone. In a separate field study, treatments consisted of no
traffic (control), foot traffic, and walk behind mower traffic (rolling) at 0700 and 0900
when canopy temperatures were at or below 0oC. Under traffic stress, on all TQ rating
dates, 0700 rolling traffic decreased TQ by ~1.1 units compared to foot traffic at 0700.
In December, regardless of traffic application time, rolling traffic reduced bentgrass shoot
growth ~17%. By the end of March, all treatments had acceptable TQ. Root TNC and
shoot chlorophyll concentrations were unaffected in May and August. This study
indicates bentgrass damage due to winter traffic is limited to winter and early spring
months and full recovery should be expected by summer.
vii
ACKNOWLEDGMENTS
I would like to sincerely thank my major advisor, mentor, and good friend, Dr.
Haibo Liu. Thank you for your support and providing me an experience of a lifetime at
Clemson University. I look forward to future collaborations. Again, many thanks.
Also, I would like to thank my committee members for all of their unique
contributions. Many thanks for my good friend, Mr. Philip Brown, for the countless
hours assisting in many of my greenhouse projects. Thank you to Mr. Bud Sarvis, Mr.
Brandon Stiglbauer, Mr. Ray McCauley, and Mr. Steven Long for their friendship and
assistance in data collection and much needed assistance in maintaining our turfgrass
research plots. Also, thanks to Dr. Wes Totten for all of his help in measuring
carbohydrates.
Much needed thanks are in order for my parents, aunt, and grandmother. Without
all of your sacrifices and support, my success would not have been possible. All of you
have provided me with every opportunity to succeed in life. Thank you all again for your
encouragement and sacrifices made during my graduate school career.
Final thanks are in order for my wife, Victoria Baldwin. Your love and support
have allowed me to complete my graduate education. I look forward to our future
adventures together.
viii
TABLE OF CONTENTS
Page
TITLE PAGE ....................................................................................................................... i
ABSTRACT ........................................................................................................................ ii
ACKNOWLEDGMENTS ................................................................................................ vii
LIST OF TABLES ............................................................................................................ xii
LIST OF FIGURES ...........................................................................................................xx
LIST OF ILLUSTRATIONS .......................................................................................... xxii
CHAPTER
I. INTRODUCTION .............................................................................................1
II. LITERATURE REVIEW ..................................................................................5
Golf Course Landscape Related to Shade ....................................................5
C3 and C4 Photosynthesis .............................................................................6
Physiological Responses of Turfgrasses Grown Under
Shade .........................................................................................................8
Light Quality ..............................................................................................13
Anatomical Responses of Turfgrasses Grown Under
Shade .......................................................................................................16
Phytochrome and Gibberellins ...................................................................17
Plant Growth Regulators ............................................................................20
Cultural Practices .......................................................................................28
III. PHYSIOLOGICAL AND MORPHOLOGICAL
RESPONSES OF 42 BERMUDAGRASS
CULTIVARS .............................................................................................36
Introduction ................................................................................................36
Materials and Methods ...............................................................................37
ix
Table of Contents (Continued)
................................................................................................................ Page
Results and Discussion ..............................................................................41
Conclusion .................................................................................................56
IV. DIVERSITY OF 42 BERMUDAGRASS CULTIVARS
IN A REDUCED LIGHT ENVIRONMENT ...........................................60
Introduction ................................................................................................60
Materials and Methods ...............................................................................62
Results ........................................................................................................65
Discussion ..................................................................................................71
Conclusion .................................................................................................75
V. DORMANT BERMUDAGRASS SPRING GREEN-UP
INFLUENCED BY SHADE......................................................................76
Introduction ................................................................................................76
Materials and Methods ...............................................................................78
Results ........................................................................................................81
Discussion ..................................................................................................89
Conclusion .................................................................................................91
VI. WINTER CULTURAL PRACTICES AND SHADE
IMPACTS ON „TIFEAGLE‟ BERMUDAGRASS
SPRING GREEN-UP.................................................................................93
Introduction ................................................................................................93
Materials and Methods ...............................................................................95
Results ........................................................................................................98
Discussion ................................................................................................101
Conclusion ...............................................................................................104
VII. MANAGEMENT PRACTICES TO ENHANCE „CHAMPION‟
BERMUDAGRASS PUTTING GREEN UNDER
SHADE ....................................................................................................105
Introduction ..............................................................................................105
x
Table of Contents (Continued)
................................................................................................................ Page
Materials and Methods .............................................................................108
Results and Discussion ............................................................................112
Conclusion ...............................................................................................124
VIII. ALTERED LIGHT SPECTRAL QUALITIES IMPACTS
ON WARM-SEASON TURFGRASS GROWTH AND
DEVELOPMENT ....................................................................................126
Introduction ..............................................................................................126
Materials and Methods .............................................................................129
Results ......................................................................................................135
Discussion ................................................................................................149
Conclusion ...............................................................................................154
IX. CREEPING BENTGRASS SEASONAL RESPONSES
TO VARIOUS WINTER LIGHT INTENSITIES ...................................155
Introduction ..............................................................................................155
Materials and Methods .............................................................................157
Results ......................................................................................................162
Discussion ................................................................................................170
Conclusion ...............................................................................................175
X. VARIOUS WINTER TRAFFIC IMPACTS ON A
„L93‟ CREEPING BENTRASS PUTTING GREEN ..............................176
Introduction ..............................................................................................176
Materials and Methods .............................................................................178
Results ......................................................................................................183
Discussion ................................................................................................188
Conclusion ...............................................................................................190
XI. SUMMARY AND PERSPECTIVES ............................................................191
APPENDICES .................................................................................................................198
A: Additional Tables and Figures .......................................................................199
xi
Table of Contents (Continued)
................................................................................................................ Page
B: Chlorophyll Extraction with DMSO ..............................................................203
C: Procedure for Nelson‟s Assay for TNC Analysis ..........................................204
D: Illustrations ....................................................................................................208
REFERENCES ................................................................................................................227
xii
LIST OF TABLES
Table ........... Page
1.1 Research history of turfgrass species responses when light
is a limiting growth factor ............................................................................3
2.1 Comparison of 31 turfgrasses shade adaptation
(Beard, 2005) .............................................................................................30
2.2 Classification of 42 bermudagrass cultivars relative shade
tolerance (adapted from Baldwin et al., 2008) ...........................................31
3.1 Spring green-up (SGU) of 42 bermudagrass cultivars rated
from 20 March to 21 April 2006 at Clemson University,
Clemson, SC ..............................................................................................42
3.2 Spring green-up (SGU) of 42 bermudagrass cultivars rated
from 20 March to 21 April 2007 at Clemson
University, Clemson, SC............................................................................44
3.3 Average weekly maximum/minimum air temperatures
(oC) and precipitation (cm) from 20 March to 27
April 2006 and 2007 in Clemson University, Clemson, SC ......................45
3.4 Turfgrass quality, clipping yield, shoot chlorophyll,
total root biomass, and thatch accumulation of 42
field-grown bermudagrass cultivars at Clemson
University in May, 2006 and 2007 ............................................................48
3.5 Turfgrass quality (TQ) of 42 bermudagrass cultivars
rated from June to August 2006 and 2007 at
Clemson University, Clemson, SC ............................................................50
3.6 Shoot chlorophyll, clipping yield, root biomass, and
thatch accumulation of 42 field-grown bermudagrass
cultivars at Clemson University in July, 2006 and 2007 ...........................52
xiii
List of Tables (continued)
Table ................................................................................................................ Page
3.7 Percent fall dormancy of 42 bermudagrass cultivars rated
from 1 November to 15 December 2006 and 2007 at
Clemson University, Clemson, SC ............................................................54
3.8 Turfgrass quality, clipping yield, shoot chlorophyll,
total root biomass, and thatch accumulation of 42
field-grown bermudagrass cultivars at Clemson
University in September, 2006 and 2007 ...................................................57
4.1 Turfgrass quality of 42 bermudagrass cultivars after
4 and 8 weeks of full-sunlight (control) and 64%
continuous shade at the Clemson University
greenhouse research complex ....................................................................66
4.2 Total shoot chlorophyll (mg g-1
) concentration of 42
bermudagrass cultivars after 4 and 8 weeks of
full-sunlight (control) and 64% continuous shade at
the Clemson University research greenhouse complex .............................68
4.3 Root length (cm) of 42 bermudagrass cultivars after
8 weeks of full-sunlight (control) and 64% continuous
shade at the Clemson University research greenhouse
complex ......................................................................................................70
4.4 Total root biomass (g) of 42 bermudagrass cultivars
after 8 weeks of full-sunlight (control) and 64%
continuous shade at the Clemson University research
greenhouse complex...................................................................................72
4.5 Overall shade tolerance rank of 42 bermudagrass
cultivars after 8 weeks of full-sunlight (control) and
64% continuous shade at the Clemson University
research greenhouse complex ....................................................................74
xiv
List of Tables (continued)
Table ................................................................................................................ Page
5.1 Spring green-up of six bermudagrass cultivars influenced
by various light regimes (full-sunlight and 55%
continuous shade) in spring, 2006 .............................................................83
5.2 Spring green-up of six bermudagrass cultivars influenced
by various light regimes (full-sunlight and 55%
continuous shade) in spring, 2007 .............................................................85
5.3 Turfgrass quality of six bermudagrass cultivars influenced
by various light regimes (full-sunlight and 55%
continuous shade) from 1 June to 31 July, 2006 and 2007 ........................87
5.4 Chlorophyll concentration (mg g-1
) and root total
non-structural carbohydrates (TNC) (mg g-1
) of
six bermudagrass cultivars influenced by various
light regimes (full-sunlight and 55% continuous shade)
in July, 2006 and 2007 ...............................................................................88
6.1 Spring green-up of 'TifEagle' bermudagrass influenced
by various winter cultural practices (colorant, overseed,
and dormant) and light intensities (full-sunlight and
55% continuous shade) recorded from 20 March to
15 May, 2006 and 2007 .............................................................................99
6.2 Turfgrass quality of 'TifEagle' bermudagrass influenced
by various winter cultural practices (colorant, overseed,
and dormant) and light intensities (full-sunlight and
55% continuous shade) from 1 June to 1 August,
2006 and 2007 ..........................................................................................100
6.3 Total shoot chlorophyll (mg g-1
) and root total non-structural
carbohydrates (TNC) (mg g-1
) of 'TifEagle' bermudagrass
influenced by various winter cultural practices
(colorant, overseed, and dormant) and light intensities
(full-sunlight and 55% continuous shade) in May and
July, 2006 and 2007 .................................................................................102
xv
List of Tables (continued)
Table ................................................................................................................ Page
7.1 Turfgrass quality of a „Champion‟ bermudagrass putting
green collected at day 1, weeks 4, 8, and 12 in response
to three nitrogen rates (147, 294, and 441 kg ha-1
yr-1
),
plant growth regulator regimes (trinexapac-ethyl at 0
and 0.02 kg ha-1
2 wk-1
), iron applications (0 and
2.7 kg Fe ha-1
2wk-1
), and two light environments
(full-sunlight and 55% full-day shade) at Clemson
University, Clemson, SC in 2006 and 2007 .............................................114
7.2 Clipping yield (g m-2
) of a „Champion‟ bermudagrass
putting green collected at weeks 6 and 12 in response
to three nitrogen rates (147, 294, and 441 kg ha-1
yr-1
),
plant growth regulator regimes (trinexapac-ethyl at 0
and 0.02 kg ha-1
2 wk-1
), and two light environments
(full-sunlight and 55% full-day shade) at Clemson
University, Clemson, SC in 2006 and 2007 .............................................117
7.3 Total shoot chlorophyll concentration (mg g-1
) of a
„Champion‟ bermudagrass putting green collected
at weeks 6 and 12 in response to three nitrogen rates
(147, 294, and 441 kg ha-1
yr-1
), plant growth regulator
regimes (trinexapac-ethyl at 0 and 0.02 kg ha-1
2 wk-1
),
and two light environments (full-sunlight and 55%
full-day shade) at Clemson University, Clemson, SC
in 2006 and 2007 ......................................................................................119
7.4 Thatch accumulation, thatch thickness, and root total
non-structural carbohydrates of a „Champion‟
bermudagrass putting green collected at week 12
in response to three nitrogen rates (147, 294, and 441
kg ha-1
2 wk-1
), plant growth regulator regimes
(trinexapac-ethyl at 0 and 0.02 kg ha-1
2 wk-1
), and
two light environments (full-sunlight and 55% shade)
at Clemson University, Clemson, SC in 2006 and 2007..........................123
xvi
List of Tables (continued)
Table ................................................................................................................ Page
8.1 Clipping yield (g m-2
), lateral spread (g), shoot
width (mm), shoot chlorophyll (mg g-1
), root
mass (g m-2
), and root length density (mm cm3),
of 'Diamond' zoysiagrass, 'Sea Isle 2000' seashore
paspalum, 'Celebration' bermudagrass, and
'Tifway' bermudagrass under full-sunlight. .............................................136
8.2 Turfgrass quality of 'Diamond' zoysiagrass, 'Sea Isle 2000'
seashore paspalum, 'Celebration' bermudagrass, and
'Tifway' bermudagrass affected by full-sunlight and
various types of filtered light (~65% reduction) in a
greenhouse study ......................................................................................139
8.3 Relative clipping yield of 'Diamond' zoysiagrass, 'Sea Isle
2000' seashore paspalum, 'Celebration' bermudagrass,
and 'Tifway' bermudagrass affected by full-sunlight
and various types of filtered light (~65% reduction)
in a greenhouse study ...............................................................................140
8.4 Relative lateral spread of 'Diamond' zoysiagrass, 'Sea Isle
2000' seashore paspalum, 'Celebration' bermudagrass,
and 'Tifway' bermudagrass affected by full-sunlight
and various types of filtered light (~65% reduction)
in a greenhouse study ...............................................................................142
8.5 Relative shoot width of 'Diamond' zoysiagrass, 'Sea Isle
2000' seashore paspalum, 'Celebration' bermudagrass,
and 'Tifway' bermudagrass affected by full-sunlight
and various types of filtered light (~65% reduction) in
a greenhouse study ...................................................................................145
xvii
List of Tables (continued)
Table ................................................................................................................ Page
8.6 Relative shoot chlorophyll concentration of 'Diamond'
zoysiagrass, 'Sea Isle 2000' seashore paspalum,
'Celebration' bermudagrass, and 'Tifway' bermudagrass
affected by full-sunlight and various types of filtered
light (~65% reduction) in a greenhouse study .........................................146
8.7 Root and shoot total non-structural carbohydrates
(mg g-1
) of 'Diamond' zoysiagrass, 'Sea Isle 2000'
seashore paspalum, 'Celebration' bermudagrass, and
'Tifway' bermudagrass affected by full-sunlight and
various types of filtered light (~65% reduction) in
a greenhouse study ...................................................................................147
8.8 Total root biomass and root length density of „Diamond‟
zoysiagrass, „Sea Isle 2000‟ seashore paspalum,
„Celebration‟ bermudagrass, and „Tifway‟
bermudagrass affected by full-sunlight and
various types of light (~65% reduction) in a
greenhouse study ......................................................................................149
9.1 Winter surface and soil temperatures (oC) and percent
light reduction recorded at solar noon four times
weekly from 1 December to 28 February in
year I and II ..............................................................................................163
9.2 Turfgrass quality of 'L93' creeping bentgrass in
December, January, and February in response
to full-sunlight and 55% and 95% morning,
afternoon, and full-day winter shade (December
to February, 2004 to 2006) and trinexapac-ethyl
(0.02 kg ha-1
) applications every two weeks from
1 December to 31 July, 2004 to 2006 ......................................................164
xviii
List of Tables (continued)
Table ................................................................................................................ Page
9.3 Turfgrass quality of 'L93' creeping bentgrass in spring
and summer in response to full-sunlight and 55%
and 95% morning, afternoon, and full-day winter
shade (December to February, 2004 to 2006) and
trinexapac-ethyl (0.02 kg ha-1
) applications every
two weeks from 1 December to 31 July, 2004 to 2006 ...........................166
9.4 Chlorophyll concentration (mg g-1
) of 'L93' creeping
bentgrass in January, February, and May in
response to full-sunlight and 55% and 95%
morning, afternoon, and full-day winter shade
(December to February, 2004 to 2006) and
trinexapac-ethyl (0.02 kg ha-1
) applications every
two weeks from 1 December to 31 July, 2004 to 2006 ...........................167
9.5 Clipping yield (g m-2
) of 'L93' creeping bentgrass in
January, February, and May in response to
full-sunlight and 55% and 95% morning,
afternoon, and full-day winter shade (December
to February, 2004 to 2006) and trinexapac-ethyl
(0.02 kg ha-1
) applications every two weeks from
1 December to 31 July, 2005 to 2006 ......................................................169
9.6 Total root biomass (g m-2
) and root total nonstructural
carbohydrates (mg g-1
) of 'L93' creeping bentgrass
in January and February in response to full-sunlight
and 55% and 95% morning, afternoon, and full-day
winter shade and trinexapac-ethyl (0.02 kg ha-1
)
applications every two weeks from 1 December to
31 July, 2005 to 2006 ...............................................................................170
10.1 Turfgrass quality of „L93‟ creeping bentgrass without
(control) and with 24 foot and rolling winter traffic
applications at 0700 or 0900 recorded after each
24 traffic application dates from 1 December 2005
and 2006 to 1 March 2006 and 2007 .......................................................184
xix
List of Tables (continued)
Table ................................................................................................................ Page
10.2 Turfgrass quality of „L93‟ creeping bentgrass without
(control) and with 24 foot and rolling winter
traffic applications at 0700 or 0900 recorded weekly
and averaged per month from March to August,
2006 and 2007 ..........................................................................................185
10.3 Clipping yield (g m-2
) of „L93‟ creeping bentgrass without
(control) and with 24 foot and rolling winter traffic
applications at 0700 or 0900 in winter, spring, and
summer months in year I and II ...............................................................186
10.4 Chlorophyll (mg g-1
) concentration of „L93‟ creeping
bentgrass without (control) and with 24 foot and
rolling winter traffic applications at 0700 or 0900
recorded in winter, spring, and summer months in
year I and II ..............................................................................................187
10.5 Soil bulk density (g cm-3
) and infiltration rates (cm h-1)
collected end of February and root total non-structural
carbohydrates (TNC) (mg g-1) collected in May
following 24 treatment application dates with and
without (control) foot and rolling traffic at 0700
or 0900 from 1 December 2005 and 2006 to
1 March 2006 and 2007 ...........................................................................187
A.1 Bermudagrass (Cynodon dactylon (L.) Pers.) cultivars
selected for a field and greenhouse study to evaluate
morphological and physiological characteristics and
shade-tolerance at the Clemson University field
research plots and greenhouse research complex ....................................199
A.2 Average monthly surface and soil (7.6 cm depth)
temperatures (oC) of „L93‟ creeping bentgrass
during each 24 traffic treatment applications at
0700, 0900, and solar noon from 1 December, 2005
and 2006 to 1 March 2006 and 2007 .......................................................201
xx
LIST OF FIGURES
Figure Page
2.1 Simplified illustration of the C3 photosynthetic
pathway (A) compared to the C4 photosynthetic
pathway (B) (Miyao, 2003)..........................................................................9
2.2 Phytochrome structure consisting of a chromophore
and polypeptide region (Taiz and Zeiger, 2006). .......................................19
2.3 Biosynthesis of Gibberellic acid (Taiz and Zeiger, 2006). ...............................21
2.4 Chemical structure, common name, and a trade name
of trinexapac-ethyl .....................................................................................24
2.5 Type II PGR, trinexapac-ethyl, interrupting the enzyme
3β-hydroxylase from converting GA20 (a) to GA1 (b) in
plant gibberellin biosynthesis ....................................................................25
2.6 Chemical structure of flurprimidol ..................................................................26
2.7 Chemical structure paclobutrazol ....................................................................27
2.8 Type II PGRs, flurprimidol and paclobutrazol, inhibiting
the enzyme kaurene oxidase from converting
ent-kaurene (a) to ent-kaurenoic (b) acid in plant
gibberellin biosynthesis .............................................................................27
5.1 Monthly precipitation (cm) from 2 March to
31 May 2006 and 2007 and historical averages in
Clemson, SC ..............................................................................................82
5.2 Average monthly maximum and minimum temperatures (oC)
from 2 March to 31 May 2006 and 2007 and historical
averages in Clemson, SC ...........................................................................82
8.1 Portion of light spectrum filtered by the shading material
selected for a greenhouse experiment ......................................................130
xxi
List of Figures (continued)
Figure ................................................................................................................ Page
A.1 Daily and historical average maximum temperatures at
Clemson University, Clemson, SC in year I and II
from 1 December to 28 February 2005 – 2007 ........................................201
A.2 Daily and historical average minimum temperatures
at Clemson University, Clemson, SC in year I and
II from 1 December to 28 February 2005 – 2007 ....................................202
C.1 Standard curve used in Nelson‟s assay for determining
total non-structural carbohydrates content in
bermudagrass and bentgrass shoots and roots .........................................207
xxii
LIST OF ILLUSTRATIONS
Illustration Page
D.1 TiftNo.5 bermudagrass anatomical features including
bundle sheath (a), mesophyll cells (b), vascular
bundle (c), and epidermal cells (d). Image recorded
on 20 December 2005 at the Clemson University
Research Park, Clemson, SC, using a SEM-Hitachi
S3500N electron microscope ...................................................................208
D.2 Overview of 42 bermudagrass cultivars from the 2002
National Turfgrass Evaluation Program located
at the Clemson University field research plots ........................................209
D.3 Spring green-up comparison of „Riviera‟ (left) and
„Tifway‟ (right) bermudagrass selected from
the 2002 National Turfgrass Evaluation Program
at the Clemson University field research
plots. Image recorded: 18 April 2006 .....................................................210
D.4 Spring green-up comparison of „Midlawn‟ (left) and
„Celebration‟ (right) bermudagrass selected from
the 2002 National Turfgrass Evaluation Program
at the Clemson University field research
plots. Image recorded: 14 April 2007 .....................................................210
D.5 Percent dormancy comparison of „Aussie Green‟
(top-left), „Celebration‟ (top-right), and „TifSport‟
(bottom) bermudagrass selected from the 2002
National Turfgrass Evaluation Program at the
Clemson University field research plots. Image
recorded: 21 November 2006...................................................................211
D.6 Overview of a greenhouse study investigating the impact
of shade on 42 bermudagrass cultivars at the
Clemson University greenhouse complex ...............................................212
xxiii
List of Illustrations (continued)
Illustration ................................................................................................................ Page
D.7 „Tifway‟ (a), „TiftNo.4‟ (b), and „Celebration‟ (c)
bermudagrass response to 5 weeks of 64% continuous
shade at the Clemson University greenhouse
research complex .....................................................................................213
D.8 Root biomass of Celebration (left) and Tifway (right)
bermudagrass following 8 weeks of 55% continuous
shade at the Clemson University greenhouse complex............................214
D.9 Overview of a shade structure to investigate the
response of bermudagrass spring transition impacted
by 55% continuous shade located at the Clemson
University field research plots .................................................................215
D.10 Comparison of „Celebration‟ grown under full-sunlight
(a) and 55% continuous shade (b), TiftNo.4 grown
under full-sunlight (c) and 55% continuous shade
(d) and „Tifway‟ grown under full-sunlight (e)
and 55% continuous shade (f) adjacent to the
Clemson University field research plots ..................................................216
D.11 Spring performance comparison of „TifEagle‟
bermudagrass treated with a colorant (left)
and untreated (right) in the winter grown
under full-sunlight. Image recorded on May 1, 2007 .............................217
D.12 Spring performance comparison of „TifEagle‟
bermudagrass overseeded in the winter grown
in full-sunlight (left) and 55% continuous
shade (right). Image recorded on May 1, 2007 .......................................217
D.13 Overview of „Champion‟ bermudagrass shade study
at the Clemson University field research plots ........................................218
xxiv
List of Illustrations (continued)
Illustration ................................................................................................................ Page
D.14 „Champion‟ bermudagrass response to 147 (a), 294
(b), and 441 (c) kg a.i. ha-1
yr-1
of nitrogen (urea)
when grown under 55% continuous shade for 8
weeks at the Clemson University field research
plots ..........................................................................................................219
D.15 „Champion‟ bermudagrass response to 147 kg a.i.
ha-1
yr-1
of nitrogen (urea) with TE (0.02 kg
ha-1
2wk-1
) (a) and 293 kg a.i. ha-1
yr-1
of nitrogen
(urea) without TE (b) when grown under 55% shade
For 8 weeks at the Clemson University field research
plots ..........................................................................................................220
D.16 Overview of a greenhouse study investigating the
impacts of different light spectral qualities on
various warm-season turfgrasses at the Clemson
University greenhouse complex ...............................................................221
D.17 Root biomass comparison of „Sea Isle 2000‟ seashore
paspalum (top-left), „Celebration‟ bermudagrass
(top-right), „Tifway‟ bermudagrass (bottom-left)
and „Diamond‟ zoysiagrass (bottom-right) grown
under full-sunlight for eight weeks in the Clemson
University greenhouse complex. Image recorded:
13 June 2007 ............................................................................................222
D.18 Visual quality comparison of „Diamond‟ zoysiagrass
(top-left), „Sea Isle 2000‟ seashore paspalum
(top-right), „Celebration‟ bermudagrass (bottom-left),
„Tifway‟ bermudagrass (bottom-right) grown under
blue shade for six weeks in the Clemson University
greenhouse complex. Image recorded: 20 August 2007 .........................223
D.19 Overview of „L93‟ creeping bentgrass putting green
shade study initiated at the Clemson University
field research plots ...................................................................................224
xxv
List of Illustrations (continued)
Illustration ................................................................................................................ Page
D.20 „L93‟ creeping bentgrass response to rolling traffic
at 0700 (a) and rolling traffic at 0900 (b) at the
Clemson University field research plots ..................................................225
D.21 „L93‟ creeping bentgrass response to rolling traffic
at 0700 (a) and foot traffic at 0700 (b) at the
Clemson University field research plots ..................................................226
1
CHAPTER I
INTRODUCTION
Golf courses consist of two plant types (turfgrass and trees) expected to perform
optimally while competing for similar resources of water, sunlight, and nutrients. In this
unnatural ecosystem, turfgrass growth and development is often inhibited. Shade, a
major physiological stress, can rapidly alter morphological characteristics of a turfgrass
stand (Langham, 1941; McBee, 1969). Turfgrasses perform poorly in reduced light
environments due to high traffic volume, daily mowing, and reduced photosynthesis. In
shade, increased disease presence adversely affects cool-season turfgrass development,
while morphological limitations, such as reduced lateral stem growth, inhibits warm-
season turfgrass development (Beard, 1997).
Altered microenvironmental factors in shade negatively affect turfgrass
performance. Extended morning dew duration on turfgrass surfaces occur because tree
water transpiration is greatest at night (Dudeck and Peacock, 1992) encouraging disease
activity due to a more succulent growth (Beard, 1965). Dense shrubbery adjacent to
turfgrass areas impair wind movement reducing transpiration rates, increasing soil
moisture content, and decreasing carbon dioxide flux (Koh et al., 2003).
Cultural practices to enhance turfgrass performance in shade include raising
mowing heights (White, 2004; Bunnell et al., 2005b), reducing nitrogen (N) rates (Burton
et al., 1959), applying plant growth regulators (PGRs) (Qian et al., 1998; Qian and
Engelke, 1999a; Ervin et al., 2004; Bunnell et al., 2005b), and watering deeply and
infrequently (Dudeck and Peacock, 1992).
2
Numerous studies have noted the shade tolerance of many warm- and cool-season
turfgrasses (Table 1.1). Although bermudagrass, the most widely grown C4 turfgrass on
an international basis (Shearman, 2006), has been extensively studied, many challenges
and questions still remain when light is a limiting growth factor. Therefore, objectives of
this dissertation were to evaluate:
Diversity of bermudagrass cultivars grown in full-sunlight and reduced irradiance,
Shade impacts on fairway-type bermudagrass spring transition from winter
dormancy,
Impacts of various winter cultural practices and shade on putting-green
bermudagrass spring transition from winter dormancy,
Cultural management practices to minimize bermudagrass putting-green decline
under shade,
Bermudagrass responses to altered light spectral qualities,
Various winter light intensities and traffic impacts on creeping bentgrass.
3
Table 1.1. Research history of turfgrass species responses when light is a
limiting growth factor.
Bahiagrass
(Paspalum
notatum)
McBee and Holt, 1966
Bentgrass
(Agrostis spp.)
McElroy et al., 2006; Ervin et al., 2004; Tegg and Lane, 2004 a
and b; Koh et al., 2003; Steinke and Stier, 2003; Goss et al.,
2002; Bell and Danneberger, 1999 a and b; Chesnel et al., 1980;
Reid, 1933
Bermudagrass
(Cynodon spp.)
Baldwin et al., 2008; Bunnell et al., 2005 a,b, and c; Miller et al.,
2005; Stanford et al., 2005; Jiang et al., 2005; Jiang et al., 2004;
Tegg and Lane, 2004 a and b; Miller and Edenfield, 2002;
Coffey and Baltensperger, 1989; Gaussoin et al., 1988; McBee,
1969; McVey et al., 1969; McBee and Holt, 1966; Burton and
Jackson, 1964; Burton et al., 1959
Bluegrass
(Poa spp.)
Gardner and Wherley, 2005; Cereti et al., 2004; Tegg and Lane,
2004 a and b; Tan and Qian, 2003; Steinke and Stier, 2003;
Cockerham et al., 2002; Stier and Rogers, 2001; Stier et al.,1999;
Gilbert and Dipaola, 1985; Chesnel et al., 1980; Wilkinson and
Beard, 1975; Wilkinson et al., 1975; Wilkinson and Beard, 1974;
McVey et al., 1969
Buffalograss
(Buchloe
dactyloides
[Nutt.] Engelm)
Wu and Harivandi, 1995; Wu, 1990
Centipedegrass
(Eremochloa
ophiuroides
[Munro.] Hack.)
Barrios et al., 1986
Fescue
(Festuca spp.)
Gardner and Wherley, 2005; Wherley et al., 2005; Tegg and
Lane, 2004 a and b; Gilbert and Dipaola, 1985; Wu et al., 1985;
Chesnel et al., 1980; Wilkinson and Beard, 1975; Wilkinson et
al., 1975; Wilkinson and Beard, 1974; McVey et al., 1969
Perennial
ryegrass
(Lolium perenne
L.)
Cereti et al., 2004; Cockerham et al., 2002; Gilbert and Dipaola,
1985
4
Table 1.1. Research history of turfgrass species responses when light is a
limiting growth factor (continued).
Seashore
paspalum
(Paspalum
vaginatum
Swartz.)
Jiang et al., 2005; Jiang et al., 2004; Jiang et al., 2003
St.
Augustinegrass
(Stenotaphrum
secundatum
[Walt.] Kuntze
Trenholm and Nagata, 2005; Trenholm et al., 2004; Barrios et
al., 1986; Peacock and Dudeck, 1981; McBee and Holt, 1966
Zoysiagrass
(Zoysia spp.)
Bunnell et al., 2005c; Cockerham et al. 2002; Qian and Engelke,
1999 a and b; Qian et al., 1998; Reis et al., 2002; Barrios et al.,
1986; McBee and Holt, 1966
5
CHAPTER II
LITERATURE REVIEW
Golf Course Landscape Related to Shade
Beard (2005) defined shade as, “a turfed or ground surface overshadowed by
plant foliage such as a tree canopy or by an opaque structure; typically the interception of
sunlight occurs.” Trees are an essential component in the golf course landscape. For
example, Tom Lively, grounds manager at Medinah Country Club, estimated more than
12,000 trees are on the 640-acre property (Hollister, 2006). Also, Beard (1997) estimated
25% of turfgrass growth is limited due to various light restrictions. Trees provide shade
for players, make land use more efficient by separating two fairways, increase golf course
difficulty, enhance aesthetic value by screening roads, cars, and buildings, protect errant
shots from hitting pedestrians or cars, and provide a natural wildlife sanctuary and habitat
for birds (Beard, 2002). However, tree roots, which often extend outward two to three
times the tree height and can grow six feet in distance per year (Swayze, 2000), out-
compete the turfgrass root system for water and nutrients. Also, tree surface roots often
encroach bunkers, damage cart paths, affect playability, and damage equipment (Kind,
1997). Trees require additional labor and expense due to branches, twigs, pine cone, and
leaf removal prior to mowing (Lilly, 1999). Meanwhile, turfgrass maintenance
negatively affects tree health. Irrigation and equipment contacting tree trunks expedites
trunk decay, herbicides can damage tree foliage, and excessive vehicular traffic during
renovation periods damage tree roots (Lilly, 1999).
6
C3 and C4 Photosynthesis
Plants are unique organisms. Aside from certain photosynthetic bacteria, plants
capture and convert solar energy into chemical energy. Photosynthetic plant material
produce inorganic compounds needed for survival by fixing carbon dioxide (CO2) and
oxidizing water to produce oxygen and carbohydrates for sustained growth and
development.
6CO2 + 6H20 ----> 6O2 + C6H12O6
Two main carbon fixation mechanisms present in plants are the Calvin cycle and
Hatch and Slack pathway (Hatch and Slack, 1966).
Calvin Cycle
The Calvin cycle is unique to C3 plant species, however, it is present in all
photosynthetic plants and is responsible for the net conversion of CO2 to carbohydrates.
It primarily occurs in the chloroplasts (stroma) parenchyma cells with many enzymatic
steps including phosphorylation, de-phosphorylation, aldolases, and reduction
mechanisms.
Three key steps for continued function of the Calvin cycle include carboxylation,
reduction, and regeneration (Taiz and Zeiger, 2006). The first stable intermediate, 3-
phosphoglycerate (3-PGA), is formed when the receptor molecule, ribulose-1,5-
bisphosphate (RuBP), is carboxylated. The first stable intermediate is then reduced using
Carbohydrate Oxygen Water Carbon dioxide
7
light reaction products adenosine triphosphate (ATP) and nicotinamide adenine
dinucleotide phosphate (NADPH) to form a carbohydrate, glyceraldehyde-3-phosphate.
Glyceraldehyde-3-phosphate then produces sucrose or starch or regenerates the acceptor
molecule, RuBP, via adenosine diphosphate (ADP) (Taiz and Zeiger, 2006).
Hatch and Slack Cycle
The Hatch and Slack cycle is typical of C4 plant species. Unique characteristics
of C4 plants include low photorespiration rates, high photosynthetic rates, and minimal
water loss due to unique anatomical features compared to C3 plant species (Illustration
D.1). Two photosynthetic tissues in C4 photosynthesis are mesophyll and bundle sheath.
Carbon dioxide is primarily fixed in mesophyll cells, while Calvin cycle intermediates
are present in the bundle sheath. Many plasmodesmata exist between bundle sheath and
mesophyll tissues providing avenues of transport maintaining this highly coordinated and
complex pathway (Taiz and Zeiger, 2006).
There are four key stages in the C4 cycle (Taiz and Zeiger, 2006). Carbon dioxide
is fixed via phosphoenolpyruvate (PEP) carboxylase to produce oxaloacetate (OAA)
which is converted to a C4 acid, malate or aspartate, in mesophyll tissue. The C4 acids
are then shuttled to the bundle sheath via plasmodesmata where CO2 is released due to
decarboxlyation of the C4 acid. The released CO2 enters the Calvin cycle and is reduced
to carbohydrate products. Following decarboxlyation of either malate or aspartate, a C3
acid (pyruvate or alanine) is formed and shuttled back to the mesophyll where the CO2
acceptor, PEP, is regenerated (Taiz and Zeiger, 2006).
8
Plants with C4 anatomy maintain adequate CO2 concentrations near ribulose
bisphosphate carboxylase/oxygenase (Rubisco), which contributes to water conservation
on hot days and a positive net carbon gain when environmental CO2 is low (Figure 2.1).
However, this unique anatomical organization requires a higher energy demand to
maintain CO2 concentration gradients compared to the Calvin cycle (Taiz and Zeiger,
2006) and may reduce C4 plant species ability to adapt to variable environments, such as
low light. Also, C4 photosynthesis requires coordinated changes between mesophyll and
bundle sheath tissues, where C3 photosynthetic tissues require minimal coordination
(Sage and McKown, 2006). Specifically, C4 plants can not readily adapt to sunflecks
(typically occur in heavily shaded environments) due to distance between mesophyll CO2
fixation reactions and bundle sheath Calvin cycle metabolites (Horton and Neufeld,
1998). Also, light is a key component regulating several C4 cycle enzymes including
PEPCase, NADP-malate dehydrogenase, and pyruvate-phosphate (Taiz and Zeiger,
2006).
Physiological Responses of Turfgrasses Grown Under Shade
Shade reduces the photosynthetic efficiency of turfgrass leaves, leaving a
turfgrass stand vulnerable to daily mowing and traffic stresses. A reduction in leaf
sunlight capture results in carbon depletion followed by a decline in quality. Therefore,
net photosynthesis must exceed respiration for a healthy turfgrass stand (Wilkinson et al.,
1975). Reports on warm- and cool-season grasses have noted significant variations in
physiological characteristics responding to shade. Photosynthetic measurements can
9
Figure 2.1. Simplified illustration of the C3 photosynthetic pathway (A) compared to the
C4 photosynthetic pathway (B) (Miyao, 2003).
include dark respiration (plant energy use), net photosynthesis (balance of lost energy
plus energy being produced), light compensation points (least amount of light required to
sustain growth), total soluble proteins (major constituent of chloroplast stroma), and
carotenoid composition.
10
Warm-season turfgrasses
Physiological responses between „Sea Isle 1‟ seashore paspalum (Paspalum
vaginatum Swartz.) and „Tifsport‟ bermudagrass (Cynodon dactylon L. X C.
transvaalensis Burtt Davy) grown in a greenhouse for 32 days with ~80 mol m-2
s-1
were
investigated by Jiang et al. (2005). The authors indicated both cultivars had reductions in
parameters measured under low light compared to high light, but Tifsport had greater
reductions than Sea Isle 1. Tifsport grown in full-sunlight increased chlorophyll a 51%,
chlorophyll b 65%, carbohydrates 66%, total soluble proteins 55%, catalase 77%, and
ascorbate peroxidase 77% compared to shade grown Tifsport. Sea Isle 1 grown under
shade increased chlorophyll a 34%, chlorophyll b 36%, carbohydrates 52%, total soluble
proteins 22%, catalase 68%, and ascorbate peroxidase 41% compared to shade-grown
TifSport. The authors attributed greater Sea Isle 1 shade-tolerance to greater levels of
chlorophyll a and b, total soluble proteins, carbohyrates, and antioxidant enzyme
activities. In a similar study, Jiang et al. (2004) noted differences within seashore
paspalum cultivars and between seashore paspalum and bermudagrass cultivars. Under
70% and 90% continuous shade, all cultivars canopy photosynthetic rates (Pn) declined.
However, Sea Isle 1 (relatively shade-tolerant) had 48% and 63% greater Pn than
TifEagle bermudagrass (relatively shade-intolerant) under 70% and 90% shade,
respectively. Sea Isle 1 also had ~22% higher TQ score at 70% and 90% shade than
TifEagle. Regardless of shade tolerance, all cultivars grown in shade showed significant
decline for Pn rates compared to full-sunlight treatments. Compared to full-sunlight, Sea
Isle 1 minimized Pn loss (6% and 26%) while TifEagle Pn was reduced by 33% and 67%
11
compared to 70% and 90% shade, respectively. Results indicate relatively shade-tolerant
cultivars are more efficient in capturing and utilizing solar energy at low light intensities.
Miller et al. (2005) reported „Floradwarf‟ bermudagrass is more carbon-use
efficient than „Tifdwarf‟ bermudagrass when maintained at low light intensities. This
suggests Floradwarf is more adapted to longer sustained growth in low light
environments. In a separate study, Floradwarf (11%), Tifdwarf (20%), and „Reesegrass‟
(120%) bermudagrass had less efficient net photosynthesis compared to TifEagle and
„Champion‟ bermudagrass at 30% continuous shade (Miller and Edenfield, 2002). In
another study, St Augustinegrass (Stenotaphrum secundatum Walt. Kuntze.) increased
Pn, while „Tiflawn' bermudagrass decreased Pn at low light intensities (Winstead and
Ward, 1974).
Cool-season turfgrasses
Similar to warm-season turfgrasses, cool-season turfgrasses also demonstrate
photosynthetic variation in response to shade. Van Huylenbroeck and Van Bockstaele
(2001) noted more shade tolerant „slender-creeping‟ (Festuca rubra spp. trichophylla)
and „chewings‟ red fescue (F. r. L. spp. commutata), „crested hairgrass‟ (Koeleria
macrantha (Ledeb.) Schultes), and „rouhstalk grass‟ (Poa pratensis L.) reached light
saturation levels at a lower light intensity than shade sensitive perennial ryegrass (Lolium
perenne L.) and „strong-creeping‟ red fescue (F. r. spp. rubra). Wilkinson et al. (1975)
noted no significant Pn, light compensation point, or light saturation level differences
between „Merion‟ Kentucky bluegrass and „Pennlawn‟ red fescue. However, Pennlawn
12
had lower dark respiration rates than Merion at low light intensities. In conclusion,
Pennlawn was able to maintain a positive CO2 balance.
McElroy et al. (2006) subjected „Crenshaw‟ creeping bentgrass (Agrostis
stolonifera L.) in a greenhouse environment to high (47.9 mol m-2
d-1
) and low (4.7 mol
m-2
d-1
) irradiance treatments. Following a seven day acclimation period in a high or low
light environment, plants were transferred from high light to low light or transferred from
low light to high light. Carotenoid pigments, zeaxanthin, antheraxanthin, violaxanthin,
neoxanthin, lutein, lutein-5,6-epoxide (epoxylutein), and -carotene, were quantified.
Under low irradiance, lutein was the prominent carotenoid present (53%). Total
xanthophyll cycle was not as prevalent under high light conditions because of an increase
in zeaxanthin and antheraxanthin. Meanwhile, 24 hours after plants were transferred to a
low light environment, increases were noted for violaxanthin, lutein, and epoxylutein.
However, this increase was transient as a decrease was observed by hour 168.
Bell and Danneberger (1999b) noted violaxanthin may be an indicator of shade
stress for „Penncross‟ creeping bentgrass. Violaxanthin concentrations continuously
decreased from full-sunlight to temporal shade (morning or afternoon) to full-day shade.
Other carotenoids measured, neoxanthin and lutein, did not show this response to reduced
light stress.
Carotenoid composition of bermudagrass, based of previous cool-season turfgrass
reports, may be an interesting physiological determinant of shade tolerance. This type of
research has been limited to cool-season turfgrasses, in particular, creeping bentgrass.
Research of warm-season turfgrasses in this area is needed.
13
In general, relatively shade-tolerant turfgrass species and cultivars have a greater
ability of assimilating carbon at reduced light intensities as indicated by increased
photosynthetic rates in shade and the ability to reach light saturation levels at reduced
light intensities. Previous studies have shown photosynthetic capabilities have varied
within bermudagrass cultivars (Miller and Edenfield, 2002; Jiang et al., 2004 and 2005;
Miller et al., 2005). However, the warm-season turfgrasses selected in these studies have
been noted for their relative poor shade-tolerance (i.e. TifSport, TifEagle, Tiflawn,
Floradwarf, and Tifdwarf). It would be interesting to note the photosynthetic capability
of relatively shade-tolerant bermudagrass cultivars compared with industry standards
(i.e., Tifway and Tifsport) lacking shade tolerance. Previous studies have also focused on
light intensity rather than light quality. The significance of light quality altering turfgrass
photosynthesis deserves further investigations.
Light Quality
A turfgrass stand under shade can be inhibited by reduced photosynthesis (Jiang
et al., 2004; Miller et al., 2005), increased disease pressure (Beard, 1965; Vargas and
Beard, 1981) due to extended morning dew duration (Dudeck and Peacock, 1992),
reduced carbohydrate production (Bunnell et al., 2005 a and c), tree root competition
(Whitcomb, 1972; Whitcomb and Roberts, 1973), and reduced lateral stem growth
(Beard, 1997). Another factor affecting turfgrass growth and development under tree
shade are various qualities of filtered light. The photosynthetic active radiation (PAR)
available for plant growth is between 400 and 700 nm with ~90% absorbed by the plant
14
with the remainder reflected at the leaf surface or transmitted through the leaf (Taiz and
Zeiger, 2006). Blue light occurs from wavelengths 400 to 500 nm, green light 500 to 600
nm, red light 600 to 700 nm, and far-red light 700 to 800 nm (Taiz and Zeiger, 2006). In
nature, trees alter spectral quality available for turfgrass development, however, limited
research has investigated the light specific tree species filter in highly maintained
turfgrass environments. Also, most shade research has focused on light quantity by
filtering shade with black neutral cloths (Bell and Danneberger, 1999b; Koh et al., 2003;
Steinke and Stier, 2003; Bunnell et al., 2005b; Baldwin et al., 2008). The effect of light
quality on turfgrass performance is lacking and deserves research.
Gaskin (1965) demonstrated using a green shade cloth (75% light reduction) had
different light quality spectrums compared to white oak (Quercus alba L.) and maple
(Acer sp.) tree shade. McBee (1969) noted post oak (Quercus stellata) canopy filtered
wavelengths between 600 to 675 nm. Using a color temperature meter, which contains
two photocells deriving light quality indicating relative amount of blue and red light,
McKee (1963) indicated dense herbaceous shade such as lambsquarter (Chenopodium
album L.), ragweed (Ambrosia trifida L.), and smartweed (Polygonum pensylvanicum L.)
depleted blue wavelengths, while trees with a high canopy filtered red wavelengths. Bell
et al. (2000) noted conifer and deciduous tree shade (R:FR<1.0) altered spectral quality
available for turfgrass growth.
Previous investigations have noted plants vary in response to light quality.
McBee (1969) filtered wavelengths between 600-675 nm and wavelengths less than 575
nm with a 30% to 40% light quantity reduction. Bermudagrass cultivars selected
15
included Tifdwarf, Tifway, „Floraturf‟, and „Common‟. Blue light minimized stem
elongation while red light enhanced stem elongation. Shorter wavelengths (blue light)
were most important for a successful turfgrass stand, while minimal red light was
necessary for normal turfgrass appearance. McVey et al. (1969) also noted blue light
significantly enhanced quality and color while reducing clipping fresh weight production
and vertical shoot elongation in „Windsor‟ Kentucky bluegrass and „Tifgreen‟
bermudagrass.
Wherley et al. (2005) subjected „Plantation‟ (shade-tolerant) and „Equinox‟
(shade-sensitive) tall fescue (Festuca arundinacea Schreb.) to ~93% light reduction with
two different light quality regimes (R:FR >1 – neutral shade or R:FR < 1 – deciduous
shade). Trees selected were primarily Acer spp. and Fraxinus spp. Both cultivars grown
in deciduous shade produced significantly less tillering (~57%), greater leaf width
(~53%), higher chlorophyll levels (~40%), and greater leaf thickness (~24%) than neutral
shade (~93% light reduction) grown cultivars. High or low R:FR ratios did not impact
root growth.
Thorough anatomical, morphological, and physiological studies of bermudagrass
cultivars in response to various light spectrums are lacking. Light quality research on
bermudagrass is necessary to assist in management strategies of highly maintained
turfgrass areas. Results from light quality research benefits turfgrass managers by
providing information on various spectral qualities affecting bermudagrass performance.
A limited number of studies have demonstrated tree species alter light spectral
quality (McKee, 1963; McBee, 1969; Bell et al., 2000). Taking results from these
16
previous studies, continued research will specify the type of light certain tree species
filter. Future light quality research will further the understanding of how bermudagrass
cultivars respond when grown under specific tree filtered light. This information will
allow turfgrass managers to make informed decisions when trees or tree limbs are
considered for removal. Finally, light quality research is the first step in providing a
blueprint for golf course design by matching turfgrass cultivars that perform well under
specific light filtered by individual tree species.
Anatomical Responses of Turfgrasses Grown Under Shade
Turfgrass leaf anatomy alterations due to shade is poorly understood. Only a
handful of studies have been conducted since the 1970‟s. Also, the attention and focus
have been cool-season turfgrasses (Allard et al., 1991; Wilkinson and Beard, 1975;
Wherley e al., 2005). Due to genetic variation and breeding efforts of bermudagrass,
anatomical responses of shade-tolerant and shade-sensitive bermudagrass cultivars are
warranted.
Wherely et al. (2005) noted Plantation and Equinox tall fescue cultivars grown
under Acer spp. and Fraxinus spp. tree species providing ~93% light reduction produced
a significantly thicker epidermis compared to full-sunlight, while percentage of air space
in mesophyll tissues and grana thickness was unaffected due to different R:FR ratios.
Wilkinson and Beard (1975) noted the anatomical effects of Merion Kentucky
bluegrass and Pennlawn red fescue in response to low light intensities. Under shade,
Pennlawn had significant increases in vascular tissue, support tissue, and cuticle layer
17
than Merion. No differences in stomata density and chloroplast number and size were
reported between the two cultivars.
Allard et al. (1991) reported tall fescue leaves grown at low irradiance had 33%
longer epidermal cells and ~25% more epidermal cells per leaf blade than the high
irradiance grown fescue. Also, stomata density significantly decreased, while volume of
epidermis, vascular bundle, and mesophyll cells all decreased at 30% shade due to
reduced leaf thickness of shade grown plants.
Based on reduction of light quantity, these studies (Allard et al., 1991; Wherley et
al., 2005; Wilkinson and Beard, 1975) were in agreement that shade decreases stomata
density and length, reduces vascular and mesophyll cells, and increases percent air space
per unit leaf area. Bermudagrass leaf anatomy variation in response to shade (light
quantity and light quantity) has yet to be investigated.
Phytochrome and Gibberellins
Phytochrome
Phytochrome is a specific protein pigment that absorbs red (Pr) (650-680 nm) and
far red (Pfr) (710-740) light, as well as blue light, exhibits photoreversible properties, and
elicits many developmental responses in plants (Taiz and Zeiger, 2006). Phytochrome is
Pr Pfr
Red light
Far-red light
18
responsible for enabling plants to sense the length of night and allow plants to grow
toward or away from light sources. Phytochrome has also been linked to influence
flowering, leaf abscission, and dormancy. The structure of phytochrome consists of two
dimer subunits: a chromophore and an apoprotein (Figure 2.2). It has been proven that
Pfr gives rise to physiological responses within plants. Quality of light, rather than
quantity of light, mostly influences the interconversion of Pfr to Pr or Pr to Pfr. A non-
shaded microenvironment is typical of Pr/Pfr ratio greater than one, indicating red light is
not absorbed by an above tree canopy. A shaded microenvironment is indicative of a
Pr/Pfr ratio less than one, indicating a tree canopy filters red light allowing Pfr light to be
absorbed by turfgrasses. The significance of phytochrome in turfgrasses has received
little attention, however, due to the many shade environments present where turfgrasses
are grown, phytochrome activity logically plays a role in turfgrass species shade
adaptation.
Gibberellins
Gibberellins (GAs) were initially discovered in Japan by rice farmers who noted a
fungal disease caused their plants to grow tall and cease seed production (Taiz and
Zeiger, 2006). Currently, 136 naturally occurring GAs exist and function by increasing
stem, internode, and root elongation, promoting flowering and pollen development,
stimulating fruit-set, and possibly playing a role in seed development (Taiz and Zeiger,
2006). Altering GA status in turfgrass is of great commercial interest as turfgrass quality,
19
Figure 2.2. Phytochrome structure consisting of a chromophore and polypeptide region
(Taiz and Zeiger, 2006).
not biomass, is the main determinant of acceptable quality for turfgrass practitioners.
Gibberellic acid synthesis occurs via the terpenoid pathway in three distinct phases, each
occurring in different cellular compartments (Taiz and Zeiger, 2006) (Figure 2.3). PPhhaassee
oonnee occurs in plastids with ent-kaurene as the end product. The specific precursor to
GAs, geranylgeranyl disphosphate (GGPP), produces ent-kaurene via ent-copalyl
diphosphate. The sseeccoonndd pphhaassee occurs in the endoplasmic reticulum. An ent-kaurene
oxidase converts ent-kaurene to ent-kaurenoic acid which is then converted to GA12, the
20
first GA produced and the precursor for all other GAs in the plant. Also, this is the site of
type II PGR activity, such as paclobutrazol, impacting turfgrass growth and development.
PPhhaassee tthhrreeee often differs not only between species, but within the same plant in different
cellular compartments in the plant. Two pathways are known to exist, non-13-
hydoxylation or 13-hydroxylation pathway. The non-13-hydoxylation pathway converts
GA12 to GA9, which ultimately produces and oxidizes the bioactive GA4. Then, GA4 is
converted to an inactive form, GA34. The 13-hydroxylation pathway converts GA53 to
the inactive GA20 which is converted to the biologically active form GA1 via 3 -
hydroxylation. This is the enzyme which trinexapac-ethyl (TE) blocks. Three main
enzymes responsible for phase three of the GA pathway are GA 20-oxidase (encoded by
SLENDER gene), GA 3-oxidase (encoded by LE gene), and GA 2-oxidase (encoded by
SLENDER gene).
Plant Growth Regulators
Plant growth regulators (PGRs), Type I or II, have become a routine management
practice in turfgrass management. Turfgrass managers are continuously looking for
effective measures to suppress vegetative vertical growth, enhance plant resistance to
stresses, and improve disease resistance with the absence or reduction of environmentally
harmful products. In response to this demand, researchers have recently evaluated a
variety of PGRs effectiveness in:
Enhancing turfgrass quality, playability, and cultural practices:
21
Figure 2.3. Biosynthesis of Gibberellic acid (Taiz and Zeiger, 2006).
22
Increase ball roll (Yelverton, 1998; Fagerness et al., 2000; McCullough et
al., 2005 a and b)
Reduce mowing frequency (Weicko, 1997; Ervin and Koski, 1998; Goss
et al., 2002; McCarty et al., 2004; Pannacci et al., 2004; Tan and Qian,
2003; McCullough et al., 2006a and b; Totten et al., 2006; Ervin et al.,
2007; McCullough et al., 2007)
Decrease weed pressure (Isrigg et al., 1998; Gibson et al., 1998; Woosley
et al., 2003; Bigelow et al., 2007)
Enhance disease resistance (Golembiewski and Danneberger, 1998;
Avison et al., 2005; Stewart et al., 2008)
Reduce turfgrass encroachment (Johnson and Duncan, 2000)
Enhance turfgrass establishment (Isgrigg and Yelverton, 1999; Reicher
and Hardebeck, 2002; Kaminski et al., 2004; Zuk and Fry, 2005;)
Mitigating environmental stresses:
Drought (Jiang and Fry, 1998; Ervin and Koski, 2001a)
Heat (Heckman et al., 2001 a and b)
Sod tensile strength (Bingaman et al., 2001)
Salinity (Nabati et al., 1994; Baldwin et al., 2006; Shahba et al., 2008)
Freezing tolerance (Richardson, 2002; Steinke and Stier, 2004)
Shade (Qian et al., 1998; Qian and Engelke, 1999a; Stier and Rogers,
2001; Goss et al., 2002; Steinke and Stier, 2003; Tegg and Lane, 2004b;
Bunnell et al., 2005b)
23
Herbicide reduction in turfgrass species transition (Williams and Burrus, 2004;
Kraft et al., 2004)
Type I PGRs
Type I PGRs includes mefluidide (N-(2,4-dimethyl-5[[(trifluoromethyl)-
sulfonyl]amino]phenyl] acetamide) and maleic hydrazide (1,2-dihydropyridazine-3,6-
dione). Mefluidide prevents mitosis (cell division) and is often used to effectively inhibit
seed-head production, however, use in high quality turfgrass areas may cause turfgrass
discoloration (Watschke and DiPaola, 1995). Mefluidide is absorbed through foliage and
may inhibit GA biosynthesis (Watschke et al., 1992). These PGRs are applicable on golf
courses to reduce steep slope or ditch mowing (McCarty, 2005).
Type II PGRs
The most frequently used type II PGR, trinexapac-ethyl (TE) (Figure 2.4) [4-
(cyclopropyl- -hydroxy-methylene)-3,5-dioxy-cyclohexanecarboxylic acid ethyl ester],
is a structural mimic of 2-oxoglutaric acid which effects most steps of GA biosynthesis
following GA12-aldehyde (Rademacher, 2000). More specifically, TE effectively inhibits
GA20 to GA1 production (Adams et al., 1992) late in the mevalonic acid pathway
suppressing shoot vertical growth (Figure 2.5). Until the release of TE, PGR use on
highly maintained turfgrass areas was limited due to potential phytotoxicity (Shepard,
2002). Undesirable characteristics included phytotoxicity of treated leaves, reduced
recuperative ability, and increased weed pressure due to reduced competition from treated
turfgrasses (McCarty, 2005).
24
Researchers have established TE increases turfgrass leaf chlorophyll
concentration (Ervin and Koski, 2001b; Heckman et al., 2001c; Stier and Rogers, 2001;
Steinke and Stier, 2003; Bunnell et al., 2005b; McCullough et al., 2006a and b) because
TE reduces cell length and increases cell density (Ervin and Koski, 2001b). Total non-
structural carbohydrates (TNC) in cool- and warm-season turfgrasses have also been
enhanced using TE (Han et al., 1998; Waltz and Whitwell, 2005; Ervin and Zhang,
2007). Fagerness and Penner (1998) demonstrated the preferred site of absorption for TE
is the plant base, while roots absorb only 5% TE after 24 hours. Therefore, any inhibition
Trinexapac-ethyl (Primo Maxx, Syngenta Chem. Co., Greensboro, NC)
Figure 2.4. Chemical structure, common name, and a trade name of trinexapac-ethyl.
25
Figure 2.5. Type II PGR, trinexapac-ethyl, interrupting the enzyme 3β-hydroxylase from
converting GA20 (a) to GA1 (b) in plant gibberellin biosynthesis.
of root growth when applying TE is correlated to reduced shoot growth. However,
Beasley et al. (2005) reported „Moonlight‟ Kentucky bluegrass root length and root
surface area decreased ~47% by week 1 following a single TE application (0.27 kg a.i.
ha-1
), but increased from week 1 to week 4 compared to nontreated plants. Also, Beasley
et al. (2007) noted that TE reduced leaf canopy area. Repeated TE applications (0.11 kg
a.i. ha-1
) do not affect thatch development, rather increase shoot density and percent green
canopy tissue (Fagerness et al., 2001).
Trinexapac-ethyl appears environmentally safe. Haith and Rossi (2003) noted 6
applications of TE (80 g ha-1
) on creeping bentgrass maintained at greens height (3.5
mm) and fairway height (11 mm) was not hazardous to aquatic life in nearby water areas
due to low LC50 levels. Also, Fagerness and Bowman (2003) stated two TE applications
at 0.05 kg a.i. ac-1
in four week intervals did not increase nitrate leaching, rather increased
root and rhizome fertility recovery. Similarly, McCullough et al. (2006a and b) reported
A B
26
a TifEagle bermudagrass putting green treated tri-weekly with TE (0.05 kg ha-1
)
enhanced nutrient recovery in belowground tissue vs. above ground tissue.
Other type II PGRs, flurprimidol (Figure 2.6) (2R,3R+2S3S)-(4-chlorophenyl)-
4,4-dimethyl-2-(1,2,4-triazol-l-y1)pentan-3-ol) and paclobutrazol (Figure 2.7) ( -(1-
methylethyl)- -[4-trifluoromethoxy)phenyl]-5-pyrimidine-methanol), inhibit oxidation of
ent-kaurene to ent-kaurenoic acid catalyzed by monooxygenases (Figure 2.8)
(Rademacher, 2000) inhibiting GA production early in the mevalonic acid pathway
(Watschke and DiPaola, 1995). These growth regulators structures are unique in that an
electron pair is located on the hybridized N heterocycle which displaces oxygen from its
Flurprimidol (Cutless, SePro Corp., Carmel, IN)
Figure 2.6. Chemical structure of flurprimidol.
27
Paclobutrazol (Trimmet, Syngenta Chem. Co., Greensboro, NC)
Figure 2.7. Chemical structure of paclobutrazol
Figure 2.8. Type II PGRs, flurprimidol and paclobutrazol, inhibiting the enzyme kaurene
oxidase from converting ent-kaurene (a) to ent-kaurenoic (b) acid in plant gibberellin
biosynthesis.
binding site at the protoheme iron inhibiting ent-kaurene oxidation (Figure 2.8)
(Rademacher, 2000). Unlike TE, paclobutrazol and flurprimidol are root absorbed rather
A B
28
than foliar absorbed. These two PGRs are most commonly used for annual bluegrass
(Poa annua L.) suppression (Woosley et al., 2003; Bell et al., 2004; Bigelow et al.,
2007). However, for Kentucky bluegrass, Stier et al. (1999) reported two flurprimidol
applications applied at treatment initiation and again at week 6 at a sub-label rate (0.56 kg
ha-1
) maintained acceptable TQ for 100 days when grown under 1.7 mol m-2
of light. A
rate higher than label recommendations (2.8 kg ha-1
) caused phytotoxicity.
Cultural Practices
The cornerstone of turfgrass management is sound agronomic practices. Three
essential turfgrass cultural practices are nutrition, water, and mowing. Appropriate
management of these cultural practices is vital for a healthy, vigorous turfgrass stand,
especially in an unfavorable microenvironment, such as reduced light. Sound agronomic
practices can mask and at times, improve turfgrass response when environmental stresses
exist. In shade, appropriate PGR use, N, and mowing practices can minimize negative
effects of tree shade. In addition, selection of turfgrass species and cultivars adapted to
shade is also a vital management decision (Tables 2.1 and 2.2).
Trinexapac-ethyl application
The goal of a turfgrass manager is to reduce clipping yield while maintaining
optimal quality. Therefore, use of the GA20 to GA1 biosynthesis inhibiting PGR, TE, has
become a routine cultural management practice to reduce mowing frequency. However,
TE has recently been investigated as a possible environmental stress reducing PGR
(Heckman et al., 2001 a and b; Richardson, 2002; Baldwin et al. 2006). In particular, TE
29
enhances TQ when applied to shade grown turfgrasses (Stier and Rogers, 2001; Goss et
al., 2002; Steinke and Stier, 2003; Tegg and Lane, 2004b; Bunnell et al., 2005b).
In shade, GA1 and GA20 production increased 47% and 30%, respectively, in
Kentucky bluegrass cultivars (Tan and Qian, 2003). This GA increase caused unwanted
excessive vertical shoot growth rapidly depleting plant carbohydrate status. Excessive
shoot growth also leads to scalping and turfgrass thinning. Turfgrass managers prefer a
dense uniform turfgrass while minimizing shoot growth. Since TE reduced GA1
production by 49% (Tan and Qian, 2003), TE is an effective management tool to combat
unfavorable shaded microenvironments often found on golf courses.
Recent studies have shown TE to be an effective management tool to enhance warm-
season turfgrass growth and development in shade. Bunnell et al. (2005b) noted TifEagle
bermudagrass grown in 4 hours of sunlight showed greater TQ scores and chlorophyll
concentration with tri-weekly TE applications (0.0393 kg a.i. ha-1
) along with
an increase in mowing height (4.7 mm). Diamond zoysiagrass (Zoysia matrella (L.)
Merr.) grown under 86% shade with monthly (0.048 kg a.i. ha-1
) and bimonthly (0.096 kg
a.i. ha-1
) TE applications significantly enhanced TQ, root production, root + rhizome
tissue TNC, and photosynthetic efficiency (Qian and Engelke, 1999a). Similarly, Qian et
al. (1998) demonstrated TE prolonged Diamond zoysiagrass acceptable TQ (>6) for 134
more days compared to nontreated under 88% shade. Also, TE treated turf had 113%
greater TNC and 50% greater canopy photosynthetic rate compared to nontreated (Qian
et al., 1998).
30
Table 2.1. Comparison of 31 turfgrasses shade adaptation (Beard, 2005)
Relative Comparison Turfgrass Scientific Name
Excellent fine-leaf fescue Festuca spp.
wood bluegrass Poa nemoralis
St. Augustinegrass
Stenotaphrum
secundatum
rough bluegrass Poa trivialis
Kikuyugrass
Pennisetum
clandestinum
Creeping bentgrass Agrostis stolonifera
supina bluegrass Poa supine
Good tufted hairgrass Deschampsia caepitosa
annual bluegrass Poa annua var. annua
Creeping bentgrass Agrostis stolonifera
tall fescue Festuca arundinacea
velvet bentgrass Agrostis canina
crested hairgrass Koeleria macrantha
colonial bentgrass Agrostis capillaris
manila zoysiagrass
Zoysia matrella var.
matrella
Japanese zoysiagrass Zoysia japonica
Mascarene zoysiagrass
Zoysia matrella var.
tenuifolia
Medium redtop bentgrass Agrostis gigantean
meadow fescue Festuca pratensis
Canada bluegrass Poa compressa
Centipedegrass Eremochloa ophiuroides
tropical Carpetgrass Anoxopus compressus
crested dog's-tailgrass Cynosurus cristatus
Poor common Carpetgrass Anoxopus fissifolius
perennial ryegrass Lolium perenne
Seashore paspalum Paspalum vaginatum
Bahiagrass Paspalum notatum
Very-poor
annual ryegrass Lolium multiflorum
Kentucky bluegrass Poa pratensis
Bermudagrasses Cynodon spp.
American Buffalograss Buchloe dactyloides
31
Table 2.2. Classification of 42 bermudagrass cultivars relative shade tolerance (adapted from
Baldwin et al., 2008).
Relative
Comparison Cultivar Propagation Scientific Name
Excellent Celebration Vegetative Cynodon dactylon x C. transvaalensis
Very-Good TiftNo.4 Vegetative C. dactylon x C. transvaalensis
TiftNo.1 Vegetative C. dactylon x C. transvaalensis
Transcontinental Seeded
Cynodon dactylon (L.) Pers. var.
dactylon
Good SWI-1003 Seeded C. dactylon (L.) Pers. var. dactylon
Sunbird Seeded C. dactylon (L.) Pers. var. dactylon
Intermediate Aussie Green Vegetative C. dactylon x C. transvaalensis
MS-Choice Vegetative C. dactylon x C. transvaalensis
Princess 77 Seeded C. dactylon (L.) Pers. var. dactylon
SWI-1045 Seeded C. dactylon (L.) Pers. var. dactylon
SWI-1041 Seeded C. dactylon (L.) Pers. var. dactylon
SWI-1012 Seeded C. dactylon (L.) Pers. var. dactylon
Fair B-14 Seeded C. dactylon (L.) Pers. var. dactylon
Riviera Seeded C. dactylon (L.) Pers. var. dactylon
SWI-1046 Seeded C. dactylon (L.) Pers. var. dactylon
TiftNo.3 Vegetative C. dactylon x C. transvaalensis
Southern Star Seeded C. dactylon (L.) Pers. var. dactylon
TiftNo.2 Seeded C. dactylon (L.) Pers. var. dactylon
Poor Sunstar Seeded C. dactylon (L.) Pers. var. dactylon
SWI-1044 Seeded C. dactylon (L.) Pers. var. dactylon
FMC-6 Seeded C. dactylon (L.) Pers. var. dactylon
Mohawk Seeded C. dactylon (L.) Pers. var. dactylon
SWI-1001 Seeded C. dactylon (L.) Pers. var. dactylon
Tifway Vegetative C. dactylon x C. transvaalensis
Midlawn Vegetative C. dactylon x C. transvaalensis
TifSport Vegetative C. dactylon x C. transvaalensis
Premier Vegetative C. dactylon x C. transvaalensis
Ashmore Vegetative C. dactylon x C. transvaalensis
CIS-CD5 Seeded C. dactylon (L.) Pers. var. dactylon
CIS-CD6 Seeded C. dactylon (L.) Pers. var. dactylon
CIS-CD7 Seeded C. dactylon (L.) Pers. var. dactylon
Panama Seeded C. dactylon (L.) Pers. var. dactylon
La Paloma Seeded C. dactylon (L.) Pers. var. dactylon
Yukon Seeded C. dactylon (L.) Pers. var. dactylon
OKC 70-18 Vegetative C. dactylon x C. transvaalensis
NuMex Sahara Seeded C. dactylon (L.) Pers. var. dactylon
32
Table 2.2. Classification of 42 bermudagrass cultivars relative shade tolerance (adapted from
Baldwin et al., 2008) (continued).
Very-poor SWI-1014 Seeded C. dactylon (L.) Pers. var. dactylon
GN-1 Vegetative C. dactylon x C. transvaalensis
Patriot Vegetative C. dactylon x C. transvaalensis
Sundevil Seeded C. dactylon (L.) Pers. var. dactylon
SR 9554 Seeded C. dactylon (L.) Pers. var. dactylon
Arizona
Common Seeded C. dactylon (L.) Pers. var. dactylon
Nitrogen
Nitrogen is the most dynamic and important nutrient for turfgrasses. Nitrogen
provides color, density, recuperative ability, and plant health when applied at adequate
rates. It has long been associated that a reduction of N input will enhance a turfgrass
stand when light interception is limited. Burton et al. (1959) reported high N (726 kg ac-
1) in 64% shade decreased „Coastal‟ bermudagrass carbohydrates by 30% and decreased
plant density and leaf area compared to low N (90 kg ac-1
). Bunnell et al. (2005b) also
noted a 39% reduction in TNC in heavily shaded TifEagle bermudagrass with additional
N (24.5 kg ha-1
(NH4)2SO4). Stanford et al. (2005) noted Tifdwarf bermudagrass
internode and leaf length significantly increased when photosynthetic photon flux density
(PPFD) was reduced from 975 to 300 mol m-2
s-1
. Also, applying Tifdwarf
bermudagrass with N at 8.1 kg ha-1
wk-1
vs. 24.4 kg ha-1
wk-1
significantly reduced leaf
length, internode length, and above ground dry matter (Stanford et al., 2005). Therefore,
reduced N rates should enhance performance in shade by reducing above ground vertical
growth.
33
Schmidt and Blaser (1967) reported „Cohansey‟ bentgrass net photosynthesis
declined along with reduced growth when fertilized with 1.0 kg N per 200 m2 every 10 to
20 days. Bell and Danneberger (1999a) stated Penncross creeping bentgrass quality was
enhanced with no N input rather than 0.11 kg urea N month-1
. Similarly, Goss et al.
(2002) reported Penncross creeping bentgrass turf cover reduced 16% with high liquid N
fertilization when grown in 80% shade.
To date, only one study has been conducted to determine the influence of N, N
type, and combination of TE and N on the performance of turfgrass in shade. Steinke and
Stier (2003) evaluated „Supranova‟ supine bluegrass, „Nuglade‟, 25% mix of „Rugby II‟,
„Kelly‟, and „NuBlue‟ Kentucky bluegrass, and Penncross creeping bentgrass response to
80% light reduction. TE applications of 0.05 kg a.i. ha-1
in 28 and 58 day intervals along
with water soluble urea as granular or liquid (12 kg N ha-1
) in 14 day intervals was
evaluated. Trinexapac-ethyl significantly enhanced all species TQ and chlorophyll in
shade. Liquid applications increased chlorophyll concentration compared to granular N
form. Nitrogen source did not affect leaf N content in creeping bentgrass. In general, fall
liquid N application was best, while granular N source was best for summer TQ.
While studies have clearly indicated reducing N in shaded environments is
beneficial, research in this area is still lacking. In particular, does N source (liquid or
granular) or combination of N sources allow bermudagrass to perform more efficiently
under shade stress? Also, will the use of TE interacting with low N rates allow a
turfgrass manager to further reduce N input in a shaded environment without a
compromise in TQ? Also, the effect of mowing height in combination with TE and N
34
source has not been investigated on warm-season species. Much of the research on N
source has focused on cool-season turfgrasses.
Mowing
Mowing height is a critical management practice for a successful turfgrass stand
grown in shade. With the release of new ultradwarf bermudagrass cultivars such as
TifEagle (Hanna and Elsner, 1999), „MiniVerde‟ (Turfgrass America Co., Granbury,
TX), „MS-Supreme‟ (Krans et al., 1999), Floradwarf (Dudeck and Murdoch, 1998), and
Champion (Brown et al., 1997), superintendents maintain daily mowing heights as low as
2.5 mm to allow for player expected green speeds. A higher mowed turfgrass enhances
leaf sunlight capture ability, turfgrass density, and increases root depth (Dudeck and
Peacock, 1992). Therefore, a raise in the height of cut should enhance shade-tolerance by
allowing a greater leaf surface for solar absorption.
Recent studies have investigated the effect raising mowing heights have on
bermudagrass response when grown in shade. A TifEagle bermudagrass green
receiving 4 hours of sunlight mowed at 4.7 mm had greater TQ and chlorophyll
concentration than the 2.5 mm mowing height maintained with 4 hours of sunlight
(Bunnell et al., 2005b). However, after 8 weeks of receiving 4 hours of sunlight, TNC
were reduced from 26.28 to 17.95 mg g-1
by raising mowing heights (Bunnell et al.,
2005b). Increased mowing heights for TifEagle, Champion, Tifdwarf, Floradwarf, and
Reesegrass bermudagrass had little effects on root biomass, however, a 4 mm mowing
height significantly improved net photosynthetic rates compared to 3 mm mowing
height (Miller and Edenfield, 2002). Also, Ries et al. (2002) noted „De Anza‟
35
zoysiagrass performed optimally in shade when mowing heights were 24 mm rather
than 12 mm.
36
CHAPTER III
PHYSIOLOGICAL AND MORPHOLOGICAL RESPONSES OF 42
BERMUDAGRASS CULTIVARS
Introduction
Bermudagrass continues to be the dominate warm-season turfgrass in warm
climatic regions of the world (Shearman, 2006). Its drought tolerance, recuperative
ability, salt tolerance, wear tolerance, aggressive stoloniferous and rhizomatous growth
habit, and overall appearance make bermudagrass an ideal turfgrass in many
environments. Although bermudagrass cultivars possess such characteristics,
bermudagrass breeding programs continue to produce new and improved cultivars.
Recently, bermudagrass breeding has produce cultivars with improved characteristics,
such as enhanced cold (Martin et al., 2007) and shade tolerance (Hanna and Maw, 2007).
Previous recent investigations have noted bermudagrass diversity among
experimental, standard, and new commercially available bermudagrass cultivars for traits
such as freeze tolerance (Anderson et al., 2007), cold tolerance (Munshaw et al., 2006),
drought tolerance (Baldwin et al., 2006), shade tolerance (Jiang et al., 2004; Bunnell et
al., 2005c; Baldwin et al., 2008; and divot recovery potential (Karcher et al., 2005).
However, few studies have provided detailed morphological and physiological
characteristics of new, experimental, and industry standard field-grown bermudagrass
cultivars.
Parameters used to access selected turfgrasses in the National Turfgrass
Evaluation Program (NTEP) typically include turfgrass quality (TQ), color, percent
37
spring green-up (SGU), percent dormancy, disease/insect occurrence, winterkill,
establishment rates, leaf texture, and density. However, parameters often excluded
include carbohydrate status, root biomass, shoot biomass, thatch accumulation, and
chlorophyll. These types of parameters would be invaluable to many within the turfgrass
industry including sod producers, sports field managers, golf course superintendents,
extension personnel, and plant breeders. While many new commercially available
bermudagrass cultivars exist, few studies have examined morphological and
physiological characteristics of these new cultivars. Therefore, objective of this research
was to evaluate and compare spring, summer, and fall performance of new and
experimental bermudagrass cultivars with current bermudagrass industry standards.
Materials and Methods
A two-year research project was conducted in 2006 and 2007 at the Clemson
University Turfgrass Research Center, Clemson, SC, 2002 bermudagrass National
Turfgrass Evaluation Program (NTEP) trials (Table A.1) (Illustration D.2). The 42
bermudagrass cultivars were planted summer, 2002 on a native clayey soil. Cultivars
were provided N at a rate of 24.4 kg ha-1
in May and September, while a N rate of 48.8
kg ha-1
was applied in June, July, and September using a complete fertilizer (16N-1.7P-
6.6K) with a slow release urea and micronutrients (kg ha-1
): Calcium, 6; Magnesium, 3;
Sulfur, 9; Boron, 0.06; Copper, 0.03; Iron, 0.3; Manganese, 0.15; Molybdenum, 0.0015;
and Zinc, 0.15. Mowing was performed three to four times weekly throughout the
growing season at a height of 1.27 cm. Irrigation was provided as needed to prevent
38
drought stress and/or wilt. Glyphosphate was sprayed in the winter over all cultivars at a
rate of 4.6 L ha-1
. Otherwise, no other pesticides, herbicides, or fungicides were provided
during the duration of the study. Also, no core aerification or topdressing program
occurred.
Data collection
Data collection included visual TQ, SGU, percent dormancy, total shoot
chlorophyll, clipping yield, thatch accumulation, root total non-structural carbohydrates,
and total root biomass.
TQ was visually rated weekly and then averaged for each month from May
through October. TQ ratings were based on color, density, texture, and uniformity of the
bermudagrass surface and rated from 1 to 9, 1 = brown, dead turfgrass, 6 = minimal
acceptable turfgrass, 9 = perfect green, healthy turfgrass.
Spring green-up was visually rated every three to four days once green tissue
emerged using a scale of 0 -100% with 0% = complete brown turfgrass and 100% =
complete green turfgrass. Similarly, percent dormancy was visually rated every three to
four days once bermudagrass cultivars started to enter dormancy using a scale of 0 -100%
with 0% = complete green turfgrass and 100% = complete brown turfgrass.
Total shoot chlorophyll (mg g-1
) was measured in mid-May, mid-July, and mid-
September eath year. Fresh clippings (minimum 0.1g) were collected from each plot and
placed in a plastic bag inside a covered bucket to prevent sunlight degradation. A 0.1 g
of clipping from each plot was placed in a glass test tube (1.0 cm in width and 14.8 cm in
length) with 10 mL of dimethyl sulfoxide (DMSO), which eliminates shoot tissue
39
grinding to extract chlorophyll (Hiscox and Israelstam, 1979). Samples were incubated
in 65 oC water on a hot plate (PC-600, Corning, Corning, NY) for 1.5 hr and continuously
shaken. Upon completion, samples were passed through filter paper (Whatman 41,
Whatman, England) and remaining extract (2 mL) transferred into cuvettes. Absorbance
values were recorded at 663 nm and 645 nm wavelengths using a spectrophotometer
(GenesysTM
20, ThermoSpectronic, Rochester, NY). Blanks were initially run and also
after every sixth sample. The following formula was used to calculate total shoot
chlorophyll: (mg g-1
) = (8.02 * D663 + 20.2 * D645) * 0.1 (Arnon, 1949).
Clipping yield (g m-2
) was collected in mid-May, mid-July, and mid-September
for both years. Shoot tissue was collected using a walk behind greens mower
(Greenmaster® 800, The Toro Company, Bloomington, MN) following two days of
growth. Following clipping collection, clippings were oven dried at 80oC for 48 hr and
weighed to quantify shoot production.
Thatch accumulation (g) was measured in mid-May, mid-July, and mid-
September for both years. A bulk density sampler extracted one 154.4 cm3 core from
each plot. Roots were clipped at the base of the thatch layer and the remaining thatch
sample was placed in an 80oC oven for 96 hrs and weighed. Thatch samples were then
placed in a muffle furnace (Benchtop Muffle Furnace LMF-A550, Omega Engineering,
Inc., Stamford, CT) at 525oC for three hrs to provide ash organic weight (Snyder and
Cisar, 2000). Samples were weighed again and then subtracted from the original dry
weight, which determined thatch accumulation (g).
40
Root TNC (mg g-1
) was analyzed mid-May and mid-July for both years. Root
tissue was harvested using a bulk density sampler which extracted 154.4 cm3 (10.2 cm in
depth) cores prior to sunrise to minimize any diurnal fluctuations. Following soil
removal, root tissue samples were stored at -75oC until freeze dried at -40
oC for two wks
to cease all metabolic activity. Samples were then ground using an A-10 plant grinder
(IKA Works, Inc., Wilmington, NC). Grounded samples were rehydrated with 100 L of
80% ethanol (EtOH) and 2 mL of 0.1 M sodium acetate buffer (pH 4.5) in glass test tubes
13 X 100 mm. Rehydrated samples were placed in boiling water for 1 hr, cooled for 1 hr
and repeated. Then, 2 mL of invertase (Sigma I-4753, 433 units mg-1
) and
amyloglucosidase (Sigma A-7255, 23,000 units g-1
) were added to solution. Samples
were placed in water bath (40 – 45oC) for three days and vortexed three times daily.
TNC analysis was analyzed using Nelson‟s Assay (1944), which determines glucose and
fructose in plant tissue (Nelson, 1944; Somogyi, 1945). A 25 L aliquot was removed
and two reagents (copper and arsenomolybdate) were added to solution. Absorbance
values were measured at 520 nm using a spectrophotometer (GenesysTM
20,
ThermoSpectronic, Rochester, NY).
Roots were extracted from the soil using a cylinder core sampler (7.5 cm in diam.
by 30 cm deep) end of May, July, and September for both years to determine total root
biomass. Once all soil was completely removed from each soil plug using tap water,
roots were clipped from the thatch base and placed in an oven (80.0 oC) for 48 hr, then
weighed. Following oven drying, roots were placed in a muffle furnace (Benchtop
Muffle Furnace LMF-A550, Omega Engineering, Inc., Stamford, CT) at 525oC for three
41
hrs to provide ash organic weight (Snyder and Cisar, 2000). Samples were weighed
again and then subtracted from the original dry weight, which determined total root
biomass (g).
Data Analysis
Treatments were arranged in a randomized complete block design with three
replications. All statistical computations were conducted using the Statistical Analysis
System (version 9.1, SAS Institute, Cary, NC). Initially, means were separated by
Fisher‟s Least Significant Difference (LSD) to determine the statistically ( ≤ 0.05) best
performing cultivar. Then, Dunnett‟s test (Dunnett, 1955) was used to compare all other
cultivars with the statistically best cultivar. Year by treatment interaction occurred for
SGU ratings and total root biomass in July; therefore, data are presented and evaluated
separately for each year. A year by treatment interaction was not noted for other
parameters; therefore, yearly data were pooled. Significant differences were not detected
for root TNC in May and July; therefore, data is not presented.
Results and Discussion
Spring Green-up
Year I
Celebration was the only cultivar in the top statistical category for all SGU rating
dates in year I (Table 3.1). Percent green tissue emergence on 20 March 2006 was
highest for Celebration (21%), MS-Choice (11%), SWI-1014 (11%), and GN-1 (11%).
By 6 April 2006, Celebration (76%), Aussie Green (48%), and Riviera (53%) had
42
Table 3.1. Spring green-up (SGU) of 42 bermudagrass cultivars rated from 20 March
to 21 April 2006 at Clemson University, Clemson, SC.
Spring Green-Up†
Cultivar 3/20/06 4/3/06 4/6/06 4/10/06 4/14/06 4/18/06 4/21/06
Celebration 21* 55* 76* 75* 81* 100* 100*
Aussie Green 3 18 48* 66* 83* 100* 100*
MS-Choice 11* 21 31 48* 63* 90* 98*
Riviera 8 25 53* 66* 80* 93* 100*
SWI-1014 11* 18 26 40* 56* 73* 78*
CIS-CD6 3 11 25 40* 60* 80* 95*
FMC-6 1 10 33 36* 53* 66* 85*
GN-1 11* 30 43 16 63* 86* 90*
La Paloma 3 8 16 33* 56* 66* 76*
Southern Star 1 15 23 46* 61* 73* 90*
Sunbird 6 21 33 50* 53* 81* 90*
SWI-1001 3 23 23 46* 71* 88* 96*
SWI-1003 5 21 33 56* 76* 93* 100*
SWI-1012 1 8 21 40* 45* 80* 93*
SWI-1041 3 15 31 53* 58* 83* 90*
SWI-1044 8 28 35 61* 63* 85* 96*
SWI-1045 1 10 20 40* 71* 83* 100*
SWI-1046 3 18 28 66* 71* 95* 100*
TiftNo.1 3 6 18 36* 65* 93* 100*
TiftNo.2 5 11 36 53* 66* 90* 100*
Transcontinental 1 8 15 31 46* 76* 93*
Yukon 1 8 13 36* 56* 78* 96*
Arizona Common 3 11 13 28 48* 66* 83*
B-14 3 11 21 25 36* 60* 83*
CIS-CD5 1 6 8 20 38* 40 73*
NuMex Sahara 3 16 16 31 46* 73* 86*
Panama 1 13 13 43* 46* 56 81*
Patriot 0 5 8 18 43* 86* 100*
Princess 77 3 18 25 60* 73* 55 93*
SR 9554 3 5 15 26 50* 56* 76*
Sundevil 1 10 23 30 60* 73* 90*
Sunstar 0 11 13 33* 28 56* 83*
TiftNo.3 1 6 18 26 46* 80* 98*
TiftNo.4 1 8 15 20 41* 76* 93*
CIS-CD7 1 5 13 25 45* 55 73*
Midlawn 0 5 6 8 21 56* 90*
OKC 70-18 1 3 5 8 26 76* 96*
Tifsport 0 5 6 16 30 63* 98*
Tifway 0 5 6 13 25 70* 100*
Ashmore 0 5 10 20 26 48 73*
43
attained greater SGU compared to other cultivars. Cultivars with slowest SGU were CIS-
CD5, Patriot, Midlawn, OKC 70-18, Tifsport, Tifway, and Premier with an average SGU
rating of 7% on 6 April 2006. Riviera showed 112% (6 April 2006) and 69% (18 April
2006) greater SGU than Princess 77. Also, Rivera showed a 7.8 (6 April 2006), 4.1 (10
April 2006), and a 2.2 (14 April 2006) unit SGU increase compared to Tifway
(Illustration D.3). Munshaw et al. (2006) reported similar results in a field study as
Riviera showed significantly quicker SGU than Princess 77 and Tifway bermudagrass.
By 18 April 2006, Celebration and Aussie Green were the first cultivars to reach 100%
SGU, closely followed by Riviera (93%), SWI-1003 (93%), TiftNo.1 (93%), MS-Choice
(90%), and TiftNo.2 (90%). On the same rating date, CIS-CD5 (40%), Princess 77
(55%), CIS-CD7 (55%), Panama (56%), Ashmore (48%), Premier (46%), and Mohawk
(43%) showed significantly slower SGU ratings compared to other cultivars. On 21 April
2006, all cultivars, except Mohawk (68%), had SGU ratings greater than 70%.
Year II
Midlawn and Premier were the only cultivars in the top statistical category for all
SGU ratings in 2007 ( Illustration D.4) (Table 3.2). However, both of these cultivars had
slow SGU ratings in 2006. This yearly variation may have occurred due to differences in
Table 3.1. Spring green-up (SGU) of 42 bermudagrass cultivars rated from 20 March to
21 April 2006 at Clemson University, Clemson, SC (continued).
Premier 0 3 8 8 28 46 71*
Mohawk 1 6 11 13 35 43 68
*Mean different from the statistically best cultivar using Dunnett‟s test ( = 0.05). †Spring green-up based on a scale of 0-100%, 0% = complete brown bermudagrass, 100% =
complete green bermudagrass.
44
Table 3.2. Spring green-up (SGU) of 42 bermudagrass cultivars rated from 20
March to 21 April 2007 at Clemson University, Clemson, SC.
Spring Green-Up†
Cultivar 3/22/07 3/29/07 4/2/07 4/5/07 4/13/07 4/20/07 4/27/07 Midlawn 16* 66* 90* 93* 51* 93* 98*
Premier 38* 83* 88* 95* 58* 86* 100*
SWI-1003 21* 56* 70* 83* 30 63* 95*
SWI-1012 10 56* 80* 90* 43* 68* 91*
SWI-1041 21* 56* 75* 80* 38 75* 85*
SWI-1045 15 50* 75* 86* 48* 75* 95*
TiftNo.4 15 41* 73* 81* 51* 70* 98*
Transcontinental 28* 60* 71* 73* 32 70* 96*
Aussie Green 31* 70* 90* 93* 33 56 98*
Celebration 23* 78* 85* 93* 36 55 91*
CIS-CD6 17 50* 80* 88* 30 60* 90*
GN-1 23* 66* 65* 73* 16 50 93*
NuMex Sahara 18 55* 63* 76* 27 61* 88*
OKC 70-18 5 22 73* 83* 68* 75* 96*
Patriot 5 40 86* 96* 68* 88* 100*
Riviera 18 51* 91* 96* 35 70* 98*
Southern Star 12 56* 66* 73* 17 60* 88*
SR 9554 15 50* 66* 85* 30 60* 93*
SWI-1001 25* 63 81* 83* 30 80* 96*
SWI-1014 15 45* 75* 83* 32 73* 96*
SWI-1046 13 60* 86* 95* 35 80* 96*
TiftNo.1 10 46* 63* 85* 17 60* 98*
Yukon 10 40 83* 91* 58* 83* 100*
Arizona
Common 8 38 60* 66* 20 60* 83*
FMC-6 10 33 55* 70* 17 58* 90*
MS-Choice 15 44* 70* 75* 20 46 86*
Princess 77 15 45* 60* 83* 35 55 86*
SWI-1044 13 56* 68* 81* 25 53 76*
Tifsport 8 35 61* 76* 37 75* 98*
TiftNo.3 15 43* 81* 88* 13 55 90*
Ashmore 7 30 61* 70* 35 53 86*
Sunbird 17 37 61* 73* 20 51 78*
Sunstar 12 32 60* 73* 18 55 81*
B-14 18 48* 50 63* 15 46 70
CIS-CD7 8 35 53* 65* 13 41 75
Sundevil 10 30 52 58 28 63* 78*
TiftNo.2 8 42 50 70* 13 46 95*
Panama 12 28 35 63* 10 35 56
45
Table 3.2. Spring green-up (SGU) of 42 bermudagrass cultivars rated from 20
March to 21 April 2007 at Clemson University, Clemson, SC (continued). CIS-CD5 7 17 30 43 12 35 73
La Paloma 5 28 33 53 13 33 68
Mohawk 7 28 50 60 17 53 73
*Mean different from the statistically best cultivar using Dunnett‟s test ( = 0.05). †Spring green-up based on a scale of 0-100%, 0% = complete brown bermudagrass,
100% = complete green bermudagrass.
air temperature for each spring (Table 3.3). In 2007, the maximum air
temperature was 12oC and 8
oC warmer from 20 March to 3 April compared to
2006. Similarly, in 2007, the minimum air temperature was 7oC and 8
oC warmer
from 20 March to 3 April compared to 2006. However, in 2006, greater
precipitation was noted than in 2007 throughout the spring, however, rainfall
totals were well below historical averages (data not shown). It is commonly
accepted that optimal temperature and soil moisture are critical requirements for
Table 3.3. Average weekly maximum/minimum air temperatures (oC) and
precipitation (cm) from 20 March to 27 April 2006 and 2007 in Clemson
University, Clemson, SC.
Maximum
Temperatures (oC)
Minimum
Temperatures (oC)
Precipitation
(cm)
2006 2007 2006 2007 2006 2007
Week 1† 11 23 2 9 0.60 0.00
Week 2 17 25 5 13 0.10 0.10
Week 3 26 21 8 6 0.30 0.10
Week 4 24 17 7 6 0.30 0.02
Week 5 27 23 14 7 0.60 0.00
Week 6 28 27 13 12 0.00 0.00 †Week 1 begins on 20 March for 2006 and 2007.
46
successful bermudagrass spring transition. Based on this research, it appears air
temperature or soil moisture may be of greater importance for bermudagrass cultivar
SGU, depending on the selected cultivar. Future research is warranted to further
elucidate whether air temperature or soil moisture is more critical for enhancing SGU.
On 5 April 2007, Sundevil, CIS-CD5, La Paloma, and Mohawk showed SGU delay
(<13%) compared to all other cultivars, while Premier, Patriot, Riviera, and SWI-1046
had SGU rating ≥95%. In Clemson, SC, from 6 April to 10 April, average minimum air
temperatures were below 0.6oC, therefore, many cultivars SGU was temporarily
inhibited. However, OKC 70-18 and Patriot were able to retain >60% green color,
despite the late freeze. This can most likely be directly attributed to their improved cold
hardiness relative to other bermudagrasses since the cold temperatures minimally
impacted SGU (Anderson et al., 2007). These cultivars may continue to find a market in
the transition zone if late freezes become a common occurrence. On the other hand,
cultivars most sensitive (<15% SGU) to the late freeze were TiftNo.3, CIS-CD7,
TiftNo.2, Panama, CIS-CD5, and La Paloma. Even with the late freeze, winterkill was
not observed for any cultivars. Only Midlawn was able to maintain SGU >90% by 20
April 2007. B-14 (70%), CIS-CD7 (75%), Panama (56%), CIS-CD5 (73%), La Paloma
(68%), and Mohawk (73%) were the only cultivars to have SGU less than 80%, while
Premier, Patriot, Tifway, and Yukon were the only cultivars to reach 100% by 27 April
2007.
While bermudagrass is considered a durable turfgrass, it is a fragile plant when
transitioning from winter dormancy into an emerging green tissue state in early spring.
47
Therefore, spring is perhaps the most critical season to optimize bermudagrass growth
and performance in preparation for the summer peak growing season in the transition
zone. Cultivars with enhanced SGU may be a very desirable trait among
bermudagrasses. However, a late freezing frost may potentially cause increased freeze
damage. Therefore, cultivars in this study with enhanced SGU may or may not be a
desirable trait depending on location.
May Performance
OKC 70-18 and SWI-1046 placed in the top statistical group for each parameter
measured in May, while CIS-CD5, GN-1, and Princess 77 placed in the top statistical
group one time during May (Table 3.4). Ashmore, B-14, CIS-CD7, Panama, Sunstar,
Arizona Common, La Paloma, Mohawk, NuMex Sahara, SR 9554, and CIS-CD5 were
the only cultivars to drop below acceptable threshold of 6 for TQ in May. Cultivars with
highest TQ scores (≥7.5) were SWI-1046, Celebration, Tifway, and TiftNo.4. MS-
Choice, SWI-1041, TiftNo.4, CIS-CD5, and Princess 77 produced significantly less
clipping yield (≤3.2 g) compared to other cultivars. Meanwhile, TifSport, Tifway,
Southern Star, and Arizona Common were the only cultivars to produce >6 g of
clippings. Lowest chlorophyll concentration was noted for Ashmore (1.45 mg g-1
), while
Celebration produced highest concentration of 3.01 mg g-1
. Industry standards, Tifway
and TifSport, produced 2.72 and 2.88 mg g-1
of chlorophyll, respectively. Cultivars with
greatest root biomass (>0.70 g) included Celebration (0.89 g), MS-Choice (0.75 g), SWI-
1014 (0.72 g), and SWI-1046 (0.72 g), while Premiere (0.27 g), Patriot (0.22 g), Arizona
48
Table 3.4. Turfgrass quality, clipping yield, shoot chlorophyll, total root
biomass, and thatch accumulation of 42 field-grown bermudagrass cultivars
at Clemson University in May, 2006 and 2007.
Cultivar
Turfgrass
Quality†
Clipping
Yield
(g)
Shoot
Chlorophyll
(mg g-1
)
Root
Biomass
(g)
Thatch
(g)
OKC 70-18 7.1* 5.58* 2.37* 0.50* 8.2*
SWI-1046 7.5* 5.43* 2.48* 0.72* 8.4*
Celebration 7.7* 4.31* 3.01* 0.89* 9.9
Midlawn 7.1* 7.39* 2.83* 0.38 6.8*
Premier 7.0* 4.62* 2.81* 0.27 8.4*
Patriot 7.3* 4.20* 2.37* 0.22 8.0*
SWI-1003 7.0* 4.31* 2.59* 0.49* 8.7
SWI-1045 7.3* 4.94* 2.74* 0.8* 10.8
TiftNo.1 7.2* 4.65* 2.71* 0.68* 8.7
TiftNo.2 7.1* 3.54* 2.88* 0.68* 9.0
TiftNo.3 6.8 4.39* 2.77* 0.67* 8.5*
Ashmore 5.8 4.76* 1.45 0.47* 7.7*
Aussie Green 7.4* 4.44* 2.52* 0.30 12.3
B-14 5.2 3.76* 1.89 0.52* 7.4*
CIS-CD7 5.8 3.89* 2.13 0.47* 8.2*
Panama 5.2 3.98* 1.69 0.48* 7.3*
Sunbird 6.4* 5.52* 2.07 0.38 8.5*
Sunstar 5.8 4.58* 2.38* 0.38 7.4*
SWI-1044 6.6 4.21* 2.41* 0.69* 9.8
Tifsport 7.4* 6.07* 2.88* 0.42 9.7
Tifway 7.9* 6.21* 2.72* 0.46 12.4
Transcontinental 6.4 5.08* 1.93 0.65* 8.4*
Yukon 6.8 3.88* 2.37* 0.43 7.5*
Arizona
Common 5.8 6.09* 1.87 0.29 6.2*
CIS-CD6 6.4 5.43* 1.83 0.36 7.7*
FMC-6 6.0 4.21* 1.75 0.39 6.9*
La Paloma 5.9 4.96* 2.02 0.35 6.8*
Mohawk 5.3 5.37* 1.93 0.55* 5.6*
MS-Choice 6.1 3.15 2.47* 0.75* 12.8
NuMex Sahara 5.6 5.61* 1.91 0.33 5.0*
Riviera 6.5 5.14* 1.61 0.51* 9.9
Southern Star 6.1 7.39* 1.91 0.47* 8.9
SR 9554 5.8 4.99* 2.08 0.26 6.6*
Sundevil 6.0 4.15* 1.86 0.36 7.4*
SWI-1001 6.9 4.88* 2.17 0.46 7.1*
SWI-1012 6.7 3.85* 2.53* 0.38 8.6
SWI-1014 6.1 5.07* 2.36 0.72* 9.6
49
Table 3.4. Turfgrass quality, clipping yield, shoot chlorophyll, total root
biomass, and thatch accumulation of 42 field-grown bermudagrass cultivars
at Clemson University in May, 2006 and 2007 (continued).
SWI-1041 6.7 3.11 2.61* 0.50 7.9*
TiftNo.4 7.6* 2.94 2.75* 0.32 9.7
GN-1 6.7 4.23* 2.33 0.28 8.8
Princess 77 6.7 3.22 2.13 0.59* 8.7
*Mean different from the statistically best cultivar using Dunnett‟s test
( = 0.05). †Turfgrass quality based on a scale of 1 – 9, 1 = brown/dead turf, 6 =
minimally acceptable turf, 9 = ideal green, healthy turf.
Common (0.29 g), SR 9554 (0.26 g), and GN-1 (0.28 g) produced least (<0.30 g) root
biomass. Baldwin et al. (2006) also reported Celebration produced greater root biomass
than Arizona Common in a greenhouse study. Greater root biomass may lead to
enhanced drought tolerance of these cultivars, however, the relative drought tolerance of
many of these cultivars remains unknown. Due to such rooting variation, large scale
screening of these bermudagrass cultivars for drought tolerance is warranted. Cultivars
with greatest thatch accumulation were MS-Choice (12.8 g), Tifway (12.4 g), and Aussie
Green (12.3 g), while NuMex Sahara (5.0 g) and Mohawk (5.6 g) produced least amount
of thatch
Summer Performance
Turfgrass quality scores of Arizona Common, Ashmore, B-14, CIS-CD5, CIS-
CD7, Mohawk, NuMex Sahara, Panama, Southern Star, Sundevil, and Sunstar were all
below acceptable threshold of 6, while all other cultivars TQ scores were greater than 6 in
June (Table 3.5). Highest TQ scores in July were TiftNo.4 (7.6) and Tifway (7.7), while
50
Table 3.5. Turfgrass quality (TQ) of 42 bermudagrass cultivars rated from
June to August, 2006 and 2007 at Clemson University, Clemson, SC.
Turfgrass Quality†
Cultivar June July August
Aussie Green 7.3 7.3* 7.0*
Celebration 7.7 7.3* 7.5*
SWI-1003 6.9 7.0* 7.5*
SWI-1045 7.3 7.3* 7.1*
SWI-1046 7.5 7.2* 7.1*
Tifsport 7.3 7.3* 6.9*
TiftNo.1 7.4 7.3* 7.1*
TiftNo.2 7.5 7.2* 7.0*
TiftNo.4 7.6 7.6* 7.5*
Tifway 7.8 7.7* 7.0*
Yukon 6.9 6.9* 6.8*
MS-Choice 6.4 6.9* 7.2*
Patriot 7.6 7.0* 7.3*
SWI-1001 7.2 6.8 6.9*
SWI-1041 6.8 7.1* 7.0*
SWI-1044 6.8 7.0* 7.0*
TiftNo.3 7.5 7.1* 6.6
GN-1 6.8 6.6 6.6
Midlawn 7.1 6.1 5.8
OKC 70-18 7.0 6.7 5.9
Premier 7.0 6.6 5.4
Princess 77 6.5 6.8 7.3*
SWI-1012 6.7 6.7 7.3*
Arizona Common 5.7 5.7 5.6
Ashmore 5.8 5.7 5.8
B-14 5.4 5.8 6.0
CIS-CD5 5.9 5.8 6.3
CIS-CD6 6.3 6.2 6.3
CIS-CD7 5.8 6.1 6.4
FMC-6 6.1 6.4 6.3
La Paloma 6.1 6.2 6.5
Mohawk 5.6 5.8 6.2
NuMex Sahara 5.7 5.8 6.0
Panama 5.4 5.6 6.0
Riviera 6.2 6.5 6.4
Southern Star 5.9 5.8 5.8
SR 9554 6.1 5.7 5.7
Sunbird 6.5 5.8 5.9
Sundevil 5.9 6.2 5.8
51
Table 3.5. Turfgrass quality (TQ) of 42 bermudagrass cultivars rated
from June to August, 2006 and 2007 at Clemson University, Clemson, SC
(continued).
Sunstar 5.9 6.1 5.8
SWI-1014 6.4 6.5 6.6
Transcontinental 6.3 6.4 6.6
*Mean different from the statistically best cultivar using Dunnett‟s test ( =
0.05). †Turfgrass quality based on a scale of 1 – 9, 1 = brown/dead turf, 6 =
minimally acceptable turf, 9 = ideal green, healthy turf.
Panama‟s TQ score was lowest (5.6). Hanna and Maw (2007) reported TiftNo.4 to have
a dark green color, which may also provide insight into its relative shade-tolerance. By
August, most TQ scores were near or above the acceptable threshold (>6). Highest TQ
scores were noted for Celebration (7.5), SWI-1003 (7.5), TiftNo.4 (7.5), Patriot (7.3),
Princess 77 (7.3), and SWI-1012 (7.3) in August.
Only TiftNo.2 placed in the top statistical category for all parameters measured in
July, 2006 and 2007 (Table 3.6). In July, Tifsport (2.70 mg g-1
), SWI-1046 (2.68 mg g-1
),
SWI-1045 (2.51 mg g-1
), and Tifway (2.51 mg g-1
) had highest chlorophyll
concentrations, while Mohawk (1.72 mg g-1
), B-14 (1.73 mg g-1
), and Arizona Common
(1.83 mg g-1
) showed lowest chlorophyll concentrations. TiftNo.2, Tift.No.1, SWI-1046,
Tifway, Midlawn, and TiftNo.4 produced the greatest amount of clipping yield (>11.5 g)
compared to other cultivars, while MS-Choice (3.93 g) and Riviera (4.26 g) had lowest
clipping yield values. Depending on the type of area where the bermudagrass is to be
used (i.e., lawn, sports field, golf course or rough area), high or low clipping yield
production may or may not be a desirable characteristic. TiftNo.2 and TiftNo.3 produced
52
Table 3.6. Shoot chlorophyll, clipping yield, root biomass, and thatch
accumulation of 42 field-grown bermudagrass cultivars at Clemson University in
July, 2006 and 2007.
Cultivar
Chlorophyll
(mg g-1
) Clipping Yield (g)
Root Biomass
(g)
Thatch
(g)
Year I Year II
TiftNo.2 2.28* 13.43* 1.03* 11.91* 8.61
TiftNo.1 2.45* 14.85* 0.75 14.98* 12.23
SWI-1046 2.68* 11.83* 0.86 11.65* 13.88
Tifway 2.51* 16.98* 0.55 15.51* 14.42
TiftNo.3 2.12* 8.64 1.62* 6.33 10.77*
SWI-1044 2.23* 10.18 0.69 9.51* 10.91*
SWI-1003 2.12* 8.38 0.71 10.43* 11.49*
OKC 70-18 2.11* 11.31 0.55 10.72* 11.49*
Midlawn 2.14* 14.01* 0.38 13.21* 8.94*
TiftNo.4 2.36* 13.01* 0.48 7.92 12.68
CIS-CD5 2.07* 5.65 0.48 3.84 10.01*
SWI-1041 2.35* 7.65 0.82 7.88 10.08*
Sunstar 2.14* 10.07 0.51 8.11 10.12*
SWI-1014 2.15* 11.33 0.63 10.43 10.22*
GN-1 2.35* 7.24 0.58 4.72 10.58*
Riviera 2.04* 4.26 0.47 4.06 11.08*
Premier 2.39* 8.25 0.27 6.65 11.11*
Celebration 2.24* 7.45 0.89 6.14 11.23*
CIS-CD7 2.04* 5.81 0.49 3.89 11.35*
Patriot 2.25* 10.71 0.25 6.81 11.35*
Transcontinental 2.08* 7.08 0.48 6.89 11.56*
SWI-1045 2.51* 7.19 0.58 7.39 12.06*
Yukon 2.09* 7.21 0.43 6.53 7.86*
Southern Star 2.13* 8.20 0.45 5.01 8.75*
SWI-1012 2.14* 6.93 0.58 7.61 9.06*
La Paloma 2.11* 6.49 0.53 4.95 9.08*
Sunbird 2.08* 5.54 0.67 4.46 12.35
MS-Choice 2.28* 3.93 0.85 4.86 13.18
Tifsport 2.70* 9.81 0.64 8.01 13.19
Aussie Green 2.19* 6.79 0.43 8.52 15.09
SR 9554 1.88 6.09 0.50 4.19 10.46*
Arizona
Common 1.83 6.91 0.51 6.02 10.68*
CIS-CD6 2.01 7.76 0.41 6.92 11.14*
SWI-1001 2.02 7.51 0.62 6.61 11.34*
Mohawk 1.72 7.96 0.53 6.85 8.06*
53
Table 3.6. Shoot chlorophyll, clipping yield, root biomass, and thatch
accumulation of 42 field-grown bermudagrass cultivars at Clemson University in
July, 2006 and 2007 (continued).
Ashmore 1.99 7.52 0.65 7.23 8.21*
Sundevil 1.97 7.51 0.31 6.19 8.27*
B-14 1.73 6.33 0.63 5.62 8.49*
FMC-6 1.99 6.59 0.51 5.48 8.94*
NuMex Sahara 1.89 6.55 0.78 5.92 9.07*
Panama 1.88 5.90 0.49 4.05 9.86*
Princess 77 1.95 9.63 0.50 8.51 12.24
*Mean different from the statistically best cultivar using Dunnett‟s test ( = 0.05).
greatest root biomass in July, 2006 compared to other cultivars. In July 2007, TiftNo.2,
TiftNo.1, SWI-1046, Tifway, SWI-1044, SWI-1003, OKC 70-18, SWI-1014, and
Midlawn produced greatest root biomass compared to other cultivars. Meanwhile, CIS-
CD5 (3.84 g) and CIS-CD7 (3.89 g) produced least total root biomass in July, 2007.
Greatest thatch accumulation occurred for TiftNo.1 (12.23 g), SWI-1046 (13.88 g),
Tifway (14.42 g), TiftNo.4 (12.68 g), Sunbird (12.35 g), MS-Choice (13.18 g), Tifsport
(13.19 g), Aussie Green (15.09 g), and Princess 77 (12.24 g) compared to other cultivars.
Yukon produced the least amount of thatch (7.86 g). This cultivar is also known for its
relative cold tolerance (Anderson et al., 2002). In this study, no cultivation or
topdressing program was initiated during the study period; therefore, it should be noted
that thatch accumulation results could vary at a site where management practices, such as
aerification and topdressing routinely occurs.
Fall Performance
SWI-1046, Tifway, Midlawn, and Tifsport were the only cultivars to place in the
top statistical ratings for maintaining green color longer into the winter (Table 3.7).
54
Table 3.7. Percent fall dormancy of 42 bermudagrass cultivars rated
from 1 November to 15 December 2006 and 2007 at Clemson
University, Clemson, SC.
Percent Fall Dormancy† (0-100%)
Cultivar Wk 1 Wk 2 Wk 3 Wk 4 Wk 5
SWI-1046 23* 20* 30* 53* 75*
Tifway 15* 11* 18* 26* 60*
Midlawn 23* 8* 21* 36* 57*
Tifsport 3* 7* 16* 28* 61*
SWI-1045 35* 23* 40* 71 82
TiftNo.3 20* 28* 35* 61 87
TiftNo.4 26* 30* 41* 58 80
Riviera 50* 50* 57* 73 95
Yukon 42* 36* 50* 81 90
Ashmore 36* 36* 55* 70 97
OKC 70-18 38* 20* 28* 60 85
SWI-1012 55 43* 55* 81 92
SWI-1014 35* 50* 66 83 93
SWI-1041 33* 57 50* 63 90
Arizona
Common 38* 67 58* 72 96
Mohawk 56 46* 53* 73 95
CIS-CD5 60 48* 60* 73 100
CIS-CD7 43* 60 56* 71 95
SR 9554 53* 53* 60 68 98
TiftNo.1 46* 60 62* 86 90
TiftNo.2 40* 56 55* 81 95
Princess 77 52 61 63* 80 93
SWI-1001 52 50 56* 63 92
Sundevil 65 63 61* 70 96
Southern Star 56 60 53* 63 98
Transcontinental 60 77 75* 88 97
Panama 71 57 55* 78 98
GN-1 60 60 51* 73 92
Premier 53 63 65* 70 90
Sunstar 62 78 66 73 96
55
Table 3.7. Percent fall dormancy of 42 bermudagrass cultivars rated
from 1 November to 15 December 2006 and 2007 at Clemson
University, Clemson, SC (continued).
B-14 62 70 71 85 100
SWI-1003 58 60 65 75 93
SWI-1044 51 57 70 83 95
NuMex Sahara 60 70 66 78 100
FMC-6 70 80 78 81 100
MS-Choice 76 73 83 88 100
CIS-CD6 70 80 85 86 100
La Paloma 46 60 68 81 98
Aussie Green 80 86 88 86 98
Patriot 70 68 73 92 100
Celebration 57 70 70 92 93
Sunbird 78 85 88 88 100
*Mean different from the statistically best cultivar using Dunnett‟s test
( = 0.05). †Percent fall dormancy based on a scale of 0-100%, 0% = complete
green bermudagrass, 100% = complete brown bermudagrass.
Celebration, Aussie Green, and MS-Choice were among the quickest cultivars to break
dormancy in the spring (Table 3.1), however, these cultivars entered dormancy early in
the fall and winter (Illustration D.5). On the 4th
and 5th
rating date, SWI-1046, Tifway,
Midlawn, and Tifsport had less brown tissue present compared to other bermudagrass
cultivars. CIS-CD5, B-14, NuMex Sahara, FMC-6, MS-Choice, CIS-CD6, Sunbird, and
Patriot were the first cultivars to reach 100% brown. Meanwhile, Midlawn was the only
cultivar by the end of the study to have less than 60% dormancy. A potential concern for
cultivars that delay entering dormancy may incur increased freeze damage. However,
recent studies reveal that increasing N rates late in the growing season to retain green
color longer into winter does not increase bermudagrass winter-kill (Richardson, 2002;
56
Munshaw et al., 2006). Therefore, cultivars with late season color retention may be a
very desirable characteristic in the transition zone.
In the fall, no cultivar placed in the top statistical category for all parameters
measured (Table 3.8). However, SWI-1003, SWI-1044, SWI-1045, SWI-1001, TiftNo.4,
Tifway, and TiftNo.2 were in the top statistical category for five of the six parameters
collected. In September, only Mohawk, Patriot, B-14, Arizona Common, and Ashmore
were below TQ acceptable threshold. In October, no cultivars TQ was higher than 7,
however, Tifway (6.9) and TiftNo.4 (6.9) maintained highest TQ scores. Shoot
chlorophyll concentrations were similar among cultivars, however, SWI-1003, SWI-
1001, TiftNo.2, SWI-1046, Princess 77, NuMex Sahara, CIS-CD6, TiftNo.1, Southern
Star, and Ashmore had significantly less chlorophyll accumulation compared to other
bermudagrass cultivars. Cultivars with greatest root biomass (>0.5 g) in the fall were
SWI-1001, TiftNo.2, SWI-1046, TiftNo.3, Transcontinental, and TiftNo.1. Cultivars
with greatest thatch accumulation (>12 g) were TiftNo.4, TiftNo.3, Tifsport, MS-Choice,
Aussie Green, Celebration, Riviera, Premier, and TiftNo.1, while Mohawk, Panama,
Arizona Common produced least amount of thatch (<8 g).
Conclusion
The future for improved bermudagrasses coming to the market seems promising.
Many experimental cultivars produced from breeding programs around the country
showed excellent results. For example, the only cultivars that placed in the top statistical
57
Table 3.8. Turfgrass quality, clipping yield, shoot chlorophyll, total root biomass,
and thatch accumulation of 42 field-grown bermudagrass cultivars at Clemson
University in September, 2006 and 2007.
Turfgrass Quality†
Cultivar September October
Clipping
Yield
(g)
Shoot
Chlorophyll
(mg g-1
)
Root
Biomass
(g) Thatch
(g)
SWI-1003
7.3* 6.4* 4.31* 1.53 0.41* 11.52*
SWI-1044
7.2* 6.1* 5.97* 1.76* 0.42 11.59*
SWI-1045
7.2* 6.4* 2.66 1.75* 0.48* 11.42*
SWI-1001
7.0* 6.1* 3.46* 1.51 0.50* 10.27*
TiftNo.4
7.5* 6.9* 6.50* 1.61* 0.46* 12.62
Tifway
7.3* 6.9* 7.02* 1.76* 0.31 11.84*
TiftNo.2
7.0* 6.2* 5.69* 1.47 0.50* 11.70*
SWI-1014
6.6 5.8 7.31* 1.67* 0.38* 9.53*
SWI-1041
6.8 6.3* 6.11* 1.65* 0.35 8.31*
SWI-1046
6.8 6.4* 4.91* 1.52 0.52* 10.47*
Princess 77
6.9* 5.8 6.21* 1.37 0.38* 9.82*
TiftNo.3
6.5 6.3* 4.09* 1.72* 0.62* 12.21
Midlawn
6.6 6.1* 5.24* 2.08* 0.23 9.05*
Tifsport
7.2* 6.5* 3.98* 1.68* 0.29 14.56
MS-Choice
7.8* 6.2* 2.56 1.91* 0.41* 13.20
Transcontinental
6.9* 5.6 3.12 1.91* 0.52* 10.53*
Aussie Green
7.4* 6.0* 4.10* 1.70* 0.14 17.35
GN-1
7.1* 6.0* 1.97 1.64* 0.20 11.32*
Celebration
7.4* 6.5* 3.14 1.76* 0.42* 12.94
Sunstar
6.0 5.0 3.54* 1.85* 0.24 8.76*
SWI-1012
7.1* 5.7 2.31 1.86* 0.32 11.43*
NuMex Sahara
6.1 5.2 4.07* 1.44 0.38* 10.07*
Mohawk
5.9 5.3 2.68* 1.69* 0.29 6.47*
Riviera
6.9* 6.0* 2.82 1.73* 0.27 12.65
CIS-CD7
6.8 5.5 2.85* 1.62* 0.34 9.86*
Panama
6.5 5.0 3.48* 1.56* 0.24 7.48*
La Paloma
6.6 5.3 3.38* 1.73* 0.33 9.99*
SR 9554
6.5 5.0 3.68* 1.82* 0.22 10.21*
Yukon
6.8 5.7 7.56* 1.68* 0.22 8.23*
Premier
6.2 6.0* 4.30* 1.74* 0.16 12.30
Patriot
5.5 4.8 7.96* 1.59* 0.09 8.03*
B-14
5.9 5.2 2.99 1.76* 0.27 8.06*
Arizona
Common
5.6 5.0 2.79 1.68* 0.21 7.57*
FMC-6
6.4 5.3 3.31 1.73* 0.34 9.42*
Sundevil
6.0 4.9 2.93 1.84* 0.29 9.34*
58
Table 3.8. Turfgrass quality, clipping yield, shoot chlorophyll, total root biomass,
and thatch accumulation of 42 field-grown bermudagrass cultivars at Clemson
University in September, 2006 and 2007 (continued).
CIS-CD5
6.7 5.7 3.14 1.83* 0.32 9.27*
CIS-CD6
6.3 5.3 4.22* 1.45 0.28 9.64*
OKC 70-18
6.5 5.8 3.21 2.14* 0.27 10.53*
TiftNo.1
6.8 5.9 6.92* 1.28 0.50* 12.55
Sunbird
6.2 4.9 3.12 1.65* 0.32 9.89*
Southern Star
6.3 5.3 3.04 1.51 0.26 10.70*
Ashmore
5.8 5.5 2.92 1.47 0.16 9.84*
*Mean different from the statistically best cultivar using Dunnett‟s test ( = 0.05). †Turfgrass quality based on a scale of 1 – 9, 1 = brown/dead turfgrass, 7 = minimally
acceptable turfgrass, 9 = ideal green, healthy turfgrass.
category for all parameters measured in spring (OKC 70-18 and SWI-1046) and summer
(TiftNo.2) were experimental turfgrasses. In the fall, with the exception of Tifway, the
only cultivars that placed in the top five of the six parameters measured were
experimental cultivars. Also, few trends emerged during the study where one cultivar
could be recommended above all others. Cultivars performance varied depending on
time of year (i.e., spring, summer, or fall). At times, the same cultivar performed
significantly different from year to year. While Tifway continues to be the industry
standard, many new cultivars possess improved traits relative to Tifway. Therefore,
when a turfgrass manager is considering establishing/renovating a turfgrass site with
bermudagrass, considerations such as traffic, soil type, light intensity, temperature stress,
water availability, water quality, fertility programs, mowing practices, topdressing
regimes, and cultivation programs should all be taken into account when selecting
bermudagrass cultivars. Future studies should investigate the establishment rates, stress
59
tolerance of these cultivars (i.e., drought, salinity, aluminum), and timing of
establishment.
60
CHAPTER IV
DIVERSITY OF 42 BERMUDAGRASS CULTIVARS IN A REDUCED LIGHT
ENVIRONMENT
Introduction
Bermudagrass‟s (Cynodon spp.), a C4 plant, growth and development is
interrupted when light interception is reduced. In shade, warm-season turfgrass decline is
attributed to morphological limitations, such as reduced lateral stem growth (Beard,
1997). A shaded micro-environment initiates excessive shoot vertical growth, depleting
turfgrass root carbohydrate status (Qian and Engelke, 1999). Previous warm- and cool-
season turfgrass evaluations have noted an increase in vertical shoot growth as shade
increases (Qian et al., 1998; Tegg and Lane, 2004a).
Characteristics of C4 plants include high growth rates, low photorespiration rates,
high photosynthetic rates, and minimal water loss due to unique anatomical features
compared to C3 plant species. C4 anatomy allows plants to maintain high levels of CO2
near ribulose bisphosphate carboxylase/oxygenase (Rubisco) allowing water conservation
on hot days and a positive net carbon gain when environmental CO2 is low. However,
this unique anatomical organization may reduce C4 plant species ability to adapt to
variable environments, such as low light, because C4 photosynthesis requires coordinated
changes between mesophyll and bundle sheath tissues, whereas C3 photosynthetic tissues
require minimal coordination (Sage and McKown, 2006). Specifically, C4 plants can not
readily adapt to sunflecks that typically occur in heavily shaded environments due to
61
distance between mesophyll CO2 fixation reactions and bundle sheath Calvin cycle
metabolites (Horton and Neufeld, 1998).
Bermudagrasses continue to be the preferred turfgrass species used in the
southern United States (McCarty and Miller, 2002; McCarty, 2005), however, its use is
often limited when optimal light interception is interrupted. For example, a „TifEagle‟
bermudagrass putting green requires 32.6 mol m-2
d-1
for acceptable (≥7) turfgrass quality
(TQ) (Bunnell et al., 2005a), while „Floradwarf‟ and „Tifdwarf‟ bermudagrass requires
38.6 mol m-2
d-1
for sustained growth (Miller et al., 2005). Cultural practices to enhance
warm-season turfgrass TQ under shade includes raising mowing heights (Bunnell et al.,
2005b; White, 2004), reducing nitrogen (N) rates (Bunnell et al., 2005b; Goss et al.,
2002; Bell and Danneberger, 1999b; Burton et al., 1959), applying plant growth
regulators (Bunnell et al., 2005b; Ervin et al., 2002; Qian et al., 1998; Qian and Engelke,
1999), and watering deeply and infrequently (Dudeck and Peacock, 1992).
Variation among C4 turfgrasses shade sensitivity has been previously investigated.
Bunnell et al. (2005c) reported „Meyer‟ Japanese zoysiagrass (Zoysia japonica Steud.)
had greatest shade tolerance maintaining acceptable TQ (>7) at 71%, „Celebration‟
bermudagrass at 58%, and „TifSport‟ and „Tifway‟ bermudagrass at 41% continuous
shade. Jiang et al. (2004) noted significant variation between seashore paspalum
(Paspalum vaginatum Swartz) and bermudagrass entries under 70% and 90% shade.
„Sea Isle 1‟ and „Temple 1‟ paspalum were shade tolerant, while TifSport and TifEagle
bermudagrass showed least shade tolerance. In a similar study, Jiang et al. (2005) also
noted greater shade tolerance of Sea Isle 1 compared to TifSport bermudagrass.
62
Gaussoin et al. (1988) noted the diversity of 32 bermudagrass cultivars under 90%
uninterrupted shade. According to results, „Boise‟, „No Mow‟, and „NM 2-13‟ were
relatively shade tolerant, while „Arizona Common‟ and „Santa Ana‟ were relatively shade
sensitive. Due to the genetic variation and diversity among existing bermudagrass
cultivars, it is critical to continue shade tolerance evaluation of new bermudagrass
cultivars. Therefore, the objectives of this research were to evaluate bermudagrass
growth and determine the diversity of 42 bermudagrass cultivars maintained at 64%
reduced irradiance.
Materials and Methods
This two-year greenhouse study was conducted from 15 June 2005 to 15 August
2005 and repeated in 2006 at Clemson University (Clemson, SC) (Illustration D.6).
Greenhouse conditions averaged 30.8oC /26.2
oC high/low air temperature and 73%
relative humidity for both years. Environmental conditions (temperature and humidity)
were maintained by an automated computer recording system (Argus Controls,
Whiterock, British Columbia V4B 3Y9).
This study consisted of two light treatments: a control (full-sunlight) and 64%
continuous shade applied daily using a neutral density, polyfiber black shade cloth
(Glenn Harp and Sons, Inc., Tucker, GA). The reduced light treatment was chosen to
identify relatively shade-tolerant bermudagrass cultivars. Shade clothes were placed on a
polyvinyl chloride (PVC) structure 15.2 cm in length and 12.7 cm in diameter with 2.5
cm diameter PVC pipes. Shade tents were 30.48 cm above the turf surface to reduce
63
early morning and late afternoon sunlight encroachment. Photon flux density ( mol m-2
s-1
) and light quality were measured on a clear, cloudless day using a quantum radiometer
(Model LI-250, LiCor, Lincoln, NE) and spectroradiameter (Model LI-1800; LiCor, Inc.,
Lincoln, NE). Surface temperatures for both treatments were recorded twice on a
clear/cloudless day using an indoor/outdoor thermometer (model# 1455, Taylor,
Oakbrook, IL).
Plugs were collected from the 2002 bermudagrass National Turfgrass Evaluation
Program (NTEP) (Table A.1) field research plots located at Clemson University and
transplanted into cone-tainers with 85% sand and 15% peat as growth media. Cone-
tainer dimensions were 25.4 cm in height and 5.1 cm in diameter. Following potting,
plugs were allowed to establish for one month prior to treatment initiation. Fertilizers
were provided at 49 kg N ha-1
every two weeks using a complete fertilizer (16N-1.7P-
6.6K) with a slow release urea and micronutrients (kg•ha-1
): Calcium, 6; Magnesium, 3;
Sulfur, 9; Boron, 0.06; Copper, 0.03; Iron, 0.3; Manganese, 0.15; Molybdenum, 0.0015;
and Zinc, 0.15. Cone-tainers were mowed at a height of 12.8 mm four times a week with
clipping removal.
Data collection was identical in year I and II. Turfgrass quality ratings were
recorded weekly based on color, density, texture, and uniformity of the bermudagrass
surface. Quality was visually evaluated from 1 to 9, 1 = brown, dead turf, 6 = minimal
acceptable turf, 9 = ideal green, healthy turf.
Root biomass (g) and length (cm) were determined at the end of the study. Roots
were extracted from the soil and thoroughly washed until all soil was removed.
64
Following soil removal, root length was measured from the base of the thatch to the
longest fully extended root present. Roots were then clipped from the base of thatch and
dried in an oven at 80.0 oC for 48 hours. Once dried, samples were weighed to determine
total root biomass.
Chlorophyll (mg g-1
) was recorded at week 4 and 8. Clippings were collected
from each cone-tainer and immediately placed in a plastic bag inside a covered bucket to
prevent sunlight degradation. Clippings were weighed (0.1g) and placed in a glass test
tube (1.0 cm in width and 14.8 cm in length) with 10 ml of dimethyl sulfoxide (DMSO)
(Hiscox and Israelstam, 1979). Samples were incubated in 65 oC water on a hot plate
(PC-600, Corning, Corning, NY) for 1.5 hours and continuously shaken. Upon
completion, samples were passed through filter paper (Whatman 41, Whatman, England)
and remaining extract (2 ml) was transferred into cuvettes. The absorbance values were
recorded at 663 nm and 645 nm wavelengths using a Spectrophotometer (GenesysTM
20,
ThermoSpectronic, Rochester, NY). The following formula was used to calculate total
chlorophyll = (8.02 * D663 + 20.2 * D645) * 0.1 (Arnon, 1949).
Data Analysis
Each treatment was replicated three times in a randomized complete block design.
Data from both years were combined as treatment by year interactions were not
significant. All statistical computations were conducted using analysis of variance
(ANOVA) within the Statistical Analysis System (SAS Institute, 2005) with means
separated by Fisher‟s Least Significance Difference (LSD) test. An alpha of 0.05 was
used to determine statistical significance.
65
Results
Micro-environment
Compared to full-sunlight, shade cloths reduced temperatures 13%, while no
difference in light quality were detected. Although light quality has been shown to
impact turfgrass growth (Wherley et. al., 2005), the focus of this study was stadium
(artificial) shade. The greenhouse glass provided an additional 9% reduction in solar
irradiance for all treatments.
Turfgrass quality
Most cultivars visual TQ scores dropped well below acceptable threshold of 6
following 4 weeks of 64% continuous shade (Table 4.1). Poorest performing cultivars
included NuMex Sahara (3.8), Arizona Common (4.2), B-14 (4.3), and Panama (4.3),
while Aussie Green (7.2), Celebration (6.5), TiftNo.4 (6.2), TiftNo.1 (6.3), Sunbird (6.2),
and Transcontinental (6.0) maintained acceptable TQ ratings following 4 weeks of 64%
shade (Illustration D.7). Industry standards, Tifway and TifSport, had TQ scores of 5.0
and 5.5, respectively. After 8 weeks of continuous 64% shade, all cultivars had severe
tissue discoloration. However, Aussie Green (5.3), TiftNo.4 (4.8), and Celebration (4.5)
maintained significantly higher TQ scores compared to Patriot (2.5), Premier (2.7),
NuMex Sahara (2.7), Panama (2.7), La Paloma (2.8), and Midlawn (2.8). In the absence
of shade, most cultivars maintained or showed near acceptable TQ by week 8.
Within week 4 TQ ratings, shade grown cultivars Transcontinental, CIS-CD6,
Aussie Green, Celebration, TiftNo.1, TiftNo.2, TiftNo.4, and Mohawk did not have
66
Table 4.1. Turfgrass quality of 42 bermudagrass cultivars after 4 and 8 weeks of full-
sunlight (control) and 64% continuous shade at the Clemson University greenhouse
research complex.
Week 4 Week 8
Cultivar Full-
Sun Shade Full-Sun Shade Rank
†
Celebration 7.5a-c‡ 6.5ab 7.3a-d A 4.5a-c B 2/2
TiftNo.4 7.3a-d 6.2a-d 7.8a A 4.8ab B 2/2
TiftNo.1 7.2b-e 6.3a-c 7.2a-d A 4.3a-d B 2/2
Transcontinental 7.0c-f 6.0a-e 6.8b-f A 4.3a-d B 2/2
SWI-1003 8.0a A§ 5.7b-f B 7.3a-d A 3.5c-i B 0/2
Sunbird 7.5a-c A 6.2a-d B 7.3a-d A 4.3a-d B 2/2
Aussie Green 7.5a-c 7.2a 7.8a A 5.3a B 2/2
MS-Choice 6.8c-g A 5.8b-e B 7.3a-d A 3.7c-h B 0/2
Princess 77 7.2b-e A 5.3b-h B 6.8b-f A 3.7c-h B 0/2
SWI-1045 7.2b-e A 5.5b-g B 7.0a-e A 3.7c-h B 0/2
SWI-1041 7.8ab A 5.3b-h B 7.3a-d A 3.5c-i B 0/2
SWI-1012 7.0c-f A 5.3b-h B 7.0a-e A 4.0b-f B 0/2
B-14 6.3f-i A 4.3g-i B 6.0fg A 3.0f-i B 0/2
Riviera 7.2b-e A 5.7b-f B 7.7ab A 3.7c-h B 0/2
SWI-1046 7.2b-e A 5.3b-h B 6.7c-f A 4.0b-f B 0/2
TiftNo.3 6.7d-h A 4.8e-i B 6.5d-f A 4.0b-f B 0/2
Southern Star 7.0c-f A 5.3b-h B 6.8b-f A 3.7c-h B 0/2
TiftNo.2 6.8c-g 5.5b-g 7.0a-e A 4.2b-e B 0/2
Sunstar 6.3f-i A 4.5f-i B 6.2e-g A 3.2e-i B 0/2
SWI-1044 6.8c-g A 5.3b-h B 7.5a-c A 4.0b-f B 0/2
FMC-6 6.5e-i A 5.0d-i B 6.7c-f A 3.5c-i B 0/2
Mohawk 6.7d-h A 5.3b-h B 6.2e-g A 3.2e-i B 0/2
SWI-1001 6.8c-g A 4.8e-i B 7.0a-e 3.8b-g B 0/2
Tifway 7.5a-c A 5.0d-i B 7.5a-c A 3.2e-i B 0/2
Midlawn 6.5e-i A 4.8e-i B 6.5d-f A 2.8g-i B 0/2
Tifsport 7.2b-e A 5.5b-g B 7.7ab A 3.3d-i B 0/2
Premier 6.7d-h A 5.2c-h B 7.3a-d A 2.7hi B 0/2
Ashmore 6.8c-g A 4.8e-i B 6.7c-f A 3.2e-i B 0/2
CIS-CD5 6.2g-j A 5.0d-i B 6.8b-f A 3.3d-i B 0/2
CIS-CD6 6.3f-i 5.2c-h 7.0a-e A 3.3d-i B 0/2
CIS-CD7 6.7d-h A 5.3b-h B 6.8b-f A 3.2e-i B 0/2
Panama 6.2g-j A 4.3g-i B 7.2a-d A 2.7hi B 0/2
La Paloma 6.0h-j A 4.5f-i B 6.7c-f A 2.8g-i B 0/2
Yukon 7.0c-f A 5.5b-g B 7.3a-d A 3.2e-i B 0/2
OKC 70-18 7.0c-f A 4.8e-i B 7.0a-e A 3.2e-i B 0/2
NuMex Sahara 5.8ij A 3.8i B 6.0fg A 2.7hi B 0/2
SWI-1014 7.5a-c A 5.5b-g B 7.2a-d A 3.2e-i B 0/2
GN-1 6.2g-j A 4.5f-i B 6.2e-g A 3.2e-i B 0/2
Patriot 6.3f-i A 4.5f-i B 6.5d-f A 2.5i B 0/2
Sundevil 6.7d-h A 5.0d-i B 6.8b-f A 3.7c-h B 0/2
SR 9554 6.3f-i A 4.8e-i B 6.7c-f A 3.0f-i B 0/2
67
Table 4.1. Turfgrass quality of 42 bermudagrass cultivars after 4 and 8 weeks of full-
sunlight (control) and 64% continuous shade at the Clemson University greenhouse
research complex (continued).
Arizona
Common 5.5j A 4.2hi B 5.5g A 3.0f-i B 0/2
†Rank indicates number of times a cultivar placed in the top statistical category when grown
under 64% shade. Greatest shade tolerance = 2/2, greatest shade sensitivity = 0/2. ‡Values within a column followed by the same letter are not significantly different at P≤0.05 by
protected LSD. §Values within a row within in each week followed by the same letter are not significantly
different at P≤0.05 by protected LSD. Turfgrass quality based on a scale of 1 – 9, 1 = brown/dead turfgrass, 6 = minimal acceptable
turfgrass, 9 = ideal green, healthy turfgrass.
significant TQ reductions compared to full-sunlight. However, within week 8, all
cultivars grown in shade had a significant TQ decline compared to full-sunlight ratings.
Chlorophyll
Significant differences occurred for shoot chlorophyll concentrations at weeks 4
and 8 (Table 4.2). The shade-grown cultivar with highest chlorophyll was TiftNo.4 at
week 4 (2.47) and week 8 (2.77), while TifSport and Arizona Common had lowest
chlorophyll concentrations at week 4 (1.54) and week 8 (1.31), respectively. SWI-1003,
SWI-1041, Princess 77, and TiftNo.1 had ~33% greater chlorophyll than Tifway,
Southern Star, GN-1, and Arizona Common at this time. By week 8, SWI-1003, SWI-
1012, SWI-1045, SWI-1046, SWI-1041, and Celebration had ~45% greater chlorophyll
when grown in shade than GN-1, SWI-1014, NuMex Sahara, OKC 70-18, B-14, and
Ashmore.
SWI-1041, TiftNo.1, and Yukon produced significantly higher chlorophyll
concentrations at week 4 when grown in shade compared to full-sunlight, however, this
response was transient (Table 4.2). Transient increases in chlorophyll content have
68
Table 4.2. Total shoot chlorophyll (mg g-1
) concentration of 42 bermudagrass cultivars after
4 and 8 weeks of full-sunlight (control) and 64% continuous shade at the Clemson
University research greenhouse complex.
Week 4 Week 8
Cultivar Full Sun Shade Full Sun Shade Rank†
Celebration 1.78b-h‡ 2.08a-e 2.64 2.24a-e 2/2
TiftNo.4 2.39a 2.47a 3.19 2.77a 2/2
TiftNo.1 1.70b-h
B§
2.15a-e
A 2.71 2.13b-f 1/2
Transcontinental 1.72b-h 1.95a-h 2.53 1.82c-j 1/2
SWI-1003 2.00b 2.30ab 2.97 2.31a-d 2/2
Sunbird 1.57d-h 1.90b-h 2.43 2.15b-f 0/2
Aussie Green 1.74b-h 1.92b-h 2.42 A 1.87c-j B 0/2
MS-Choice 1.89b-d 2.07a-e 2.24 1.75e-j 1/2
Princess 77 1.67b-h 2.22a-d 2.54 2.09b-h 1/2
SWI-1045 1.76b-h 2.10a-e 2.34 2.36a-c 2/2
SWI-1041 1.84b-f
B
2.29a-c
A 2.97 2.24a-e 2/2
SWI-1012 1.88b-d 1.95b-h 2.78 2.60ab 1/2
B-14 1.46gh 1.83d-h 2.45 A 1.69e-j B 0/2
Riviera 1.71b-h 1.91b-h 2.64 1.98c-i 0/2
SWI-1046 1.96bc 2.06b-e 2.75 A 2.22b-e B 0/2
TiftNo.3 1.48f-h 1.90b-h 2.13 2.13b-f 0/2
Southern Star 1.45gh 1.78e-h 2.18 2.11b-h 0/2
TiftNo.2 1.71b-h 1.93b-h 2.82 2.12b-g 0/2
Sunstar 1.42h 1.79e-h 2.19 1.88c-j 0/2
SWI-1044 1.93b-d 2.04b-f 2.58 2.03c-h 0/2
FMC-6 1.65b-h 1.85d-h 2.22 1.92c-j 0/2
Mohawk 1.50e-h 1.78e-h 2.18 2.06b-h 0/2
SWI-1001 1.89b-d 1.93b-h 2.33 1.90c-j 0/2
Tifway 1.84b-f 1.60gh 2.61 1.84c-j 0/2
Midlawn 1.83b-g 1.93b-h 2.57 A 1.95c-j B 0/2
Tifsport 1.81b-g 1.54h 2.56 1.98c-i 0/2
Premier 2.01b 1.93b-h 2.84 A 1.74e-j B 0/2
Ashmore 1.87b-e 1.85d-h 2.62 A 1.47ij B 0/2
CIS-CD5 1.78b-h 1.89b-h 2.55 A 1.82c-j B 0/2
CIS-CD6 1.56d-h 1.81d-h 2.24 1.71e-j 0/2
CIS-CD7 1.60c-h 1.87d-h 2.32 1.80d-j 0/2
Panama 1.80b-h 1.86d-h 2.52 A 1.77d-j B 0/2
La Paloma 1.67b-h 1.85d-h 2.14 A 1.68f-j B 0/2
Yukon 1.58d-h
B
1.88c-h
A 2.48 A 1.85c-j B 0/2
OKC 70-18 1.97bc 1.95-f 2.7 A 1.67f-j B 0/2
NuMex Sahara 1.85b-f 1.98b-g 2.52 A 1.56h-j B 0/2
69
Table 4.2. Total shoot chlorophyll (mg g-1
) concentration of 42 bermudagrass cultivars after
4 and 8 weeks of full-sunlight (control) and 64% continuous shade at the Clemson
University research greenhouse complex (continued).
SWI-1014 1.74b-h 1.85d-h 2.78 A 1.58g-j B 0/2
GN-1 1.88b-d 1.74e-h 2.48 A 1.67f-j B 0/2
Patriot 1.82b-g 1.86d-h 2.55 A 1.73e-j B 0/2
Sundevil 1.61c-h 1.88c-h 2.36 2.19b-f 0/2
SR 9554 1.69b-h 1.91b-h 2.38 1.78d-j 0/2
Arizona Common 1.62c-h 1.63f-h 2.09 1.43j 0/2 †Rank indicates number of times a cultivar placed in the top statistical category when grown under
64% shade. Greatest shade tolerance = 2/2, greatest shade sensitivity = 0/2. ‡Values within a column followed by the same letter are not significantly different at P≤0.05 by protected
LSD.
§Values within a row within each week followed by the same letter are not significantly different at P≤0.05 by
protected LSD.
previously been reported under other environmental stresses (Jiang and Huang, 2001).
Within week 8, many cultivars chlorophyll concentration declined. Compared to
full-sunlight, shade-grown cultivars Ashmore, SWI-1014, B-14, and Premier, had a
~66% decline in chlorophyll, while SWI-1046, La Paloma, Aussie Green, and Midlawn
showed a ~28% chlorophyll reduction.
Root Length
Overall, root length was least affected by shade compared to other parameters
measured. No significant differences were noted for root length when grown in full-
sunlight (Table 4.3). Cultivars grown under 64% shade exhibited some statistically
different root lengths. Most striking differences were TiftNo.2 producing 89% greater
root length than Arizona Common, while SWI-1014 had a 57% root length reduction
compared to Riviera. Shade-grown Arizona Common, SWI-1014, and Sundevil, had
63%, 59%, and 41% decreases, respectively, compared their sun-grown counterparts.
70
Table 4.3. Root length (cm) of 42 bermudagrass cultivars after 8
weeks of full-sunlight (control) and 64% continuous shade at the
Clemson University research greenhouse complex.
Cultivar Sun Shade Rank†
Celebration 8.78 7.00a-d‡ 1/1
TiftNo.4 9.23 8.72a-d 1/1
TiftNo.1 9.20 8.27a-e 1/1
Transcontinental 9.62 A§ 8.40a-e B 1/1
SWI-1003 8.87 8.97ab 1/1
Sunbird 9.43 8.30a-e 1/1
Aussie Green 9.35 8.91ab 1/1
MS-Choice 8.76 8.70a-d 1/1
Princess 77 9.78 8.08a-e 1/1
SWI-1045 9.47 8.18a-e 1/1
SWI-1041 9.93 A 8.52a-e B 1/1
SWI-1012 9.13 8.37a-e 1/1
B-14 9.45 8.90a-c 1/1
Riviera 9.52 9.03ab 1/1
SWI-1046 9.58 A 8.00a-e B 1/1
TiftNo.3 9.32 8.52a-e 1/1
Southern Star 9.53 9.25ab 1/1
TiftNo.2 9.43 9.60a 1/1
Sunstar 8.85 6.67c-g 0/1
SWI-1044 9.45 8.80a-c 1/1
FMC-6 9.10 7.60a-f 1/1
Mohawk 9.42 A 7.74a-f B 1/1
SWI-1001 9.08 8.42a-e 1/1
Tifway 9.45 8.63a-d 1/1
Midlawn 9.22 7.63a-f 1/1
Tifsport 10.23 A 8.87a-c B 1/1
Premier 8.70 8.78a-d 1/1
Ashmore 9.92 7.85a-f 1/1
CIS-CD5 10.13 A 8.28a-e B 1/1
CIS-CD6 9.45 8.33a-e 1/1
La Paloma 8.83 7.45a-f 1/1
Yukon 8.80 7.73a-f 1/1
OKC 70-18 8.30 8.75a-d 1/1
NuMex Sahara 9.32 7.50a-f 1/1
SWI-1014 9.15 A 5.75fg B 0/1
GN-1 8.97 7.05b-g 0/1
Patriot 8.39 6.37e-g 0/1
Sundevil 9.23 A 6.55d-g B 0/1
71
Table 4.3. Root length (cm) of 42 bermudagrass cultivars after 8
weeks of full-sunlight (control) and 64% continuous shade at the
Clemson University research greenhouse complex (continued).
SR 9554 8.5 A 6.28e-g B 0/1
Arizona Common 8.3 A 5.08g B 0/1 †Rank indicates number of times a cultivar placed in the top statistical
category when grown under 64% shade. Greatest shade tolerance = 1/1,
greatest shade sensitivity = 0/1. ‡Values within a column followed by the same letter are not
significantly different at P≤0.05 by protected LSD. §Values within a row followed by the same letter are not significantly
different at P≤0.05 by protected LSD.
Root Biomass
Each cultivar, regardless of shade tolerance or sensitivity, had a significant
reduction in root biomass (Table 4.4). Under shade, cultivars with least root mass
reduction (~121%) included B-14, NuMex Sahara, TiftNo.3, and MS-Choice, while
cultivars with greatest root mass decline (~325%) included SWI-1001, SR9554, and
Yukon, compared to full-sun. In addition, shade-grown SR9554 had a 265% decrease in
root biomass compared to SWI-1003. Celebration and TiftNo.2 also produced ~124%
greater root biomass when grown in shade compared to Arizona Common and GN-1
(Illustration D8).
Discussion
These results suggest great potential for future breeding programs the focus on
shade-tolerance improvement of bermudagrass. Bermudagrass cultivars, especially
newer ones, demonstrated great diversity. Based on rank for TQ, chlorophyll, root
72
Table 4.4. Total root biomass (g) of 42 bermudagrass cultivars after 8
weeks of full-sunlight (control) and 64% continuous shade at the Clemson
University research greenhouse complex.
Cultivar Full Sun Shade Rank†
Celebration 0.201ab‡ A
§ 0.064a-e B 1/1
TiftNo.4 0.127d-l A 0.049b-m B 0/1
TiftNo.1 0.207a A 0.053a-k B 1/1
Transcontinental 0.179a-d A 0.067a-c B 1/1
SWI-1003 0.175a-e A 0.073a B 1/1
Sunbird 0.178a-d A 0.056a-j B 1/1
Aussie Green 0.095i-m A 0.038f-o B 0/1
MS-Choice 0.161a-h A 0.069ab B 1/1
Princess 77 0.173a-f A 0.059a-h B 1/1
SWI-1045 0.146b-j A 0.044c-m B 0/1
SWI-1041 0.149b-i A 0.048b-m B 0/1
SWI-1012 0.163a-h A 0.056a-j B 1/1
B-14 0.116f-m A 0.051a-l B 1/1
Riviera 0.189a-c A 0.061a-f B 1/1
SWI-1046 0.147b-j A 0.052a-l B 1/1
TiftNo.3 0.127d-l A 0.060a-g B 1/1
Southern Star 0.187a-c A 0.058a-i B 1/1
TiftNo.2 0.155a-h A 0.066a-d B 1/1
Sunstar 0.170a-g A 0.052a-l B 1/1
SWI-1044 0.126d-l A 0.045b-n B 0/1
FMC-6 0.113g-m A 0.050b-m B 0/1
Mohawk 0.124d-m A 0.041e-o B 0/1
SWI-1001 0.162a-h A 0.037g-o B 0/1
Tifway 0.118e-m A 0.041e-o B 0/1
Midlawn 0.067m A 0.025no B 0/1
Tifsport 0.146b-j A 0.042e-o B 0/1
Premier 0.091j-m A 0.032k-o B 0/1
Ashmore 0.163a-h A 0.041e-o B 0/1
CIS-CD5 0.133c-k A 0.033j-o B 0/1
CIS-CD6 0.095i-m A 0.036h-o B 0/1
Yukon 0.147b-j A 0.034j-o b 0/1
OKC 70-18 0.088k-m A 0.027m-o B 0/1
NuMex Sahara 0.085k-m A 0.040f-o B 0/1
SWI-1014 0.164a-h A 0.038g-o B 0/1
GN-1 0.108h-m A 0.029l-o B 0/1
Patriot 0.076lm A 0.030k-o B 0/1
Sundevil 0.110h-m A 0.043d-o B 0/1
73
Table 4.4 Total root biomass (g) of 42 bermudagrass cultivars after 8 weeks
of full-sunlight (control) and 64% continuous shade at the Clemson
University research greenhouse complex (continued).
SR 9554 0.081k-m A 0.020o B 0/1
Arizona Common 0.085k-m A 0.029l-o B 0/1 †Rank indicates number of times a cultivar placed in the top statistical category
when grown under 64% shade. Greatest shade tolerance = 1/1, greatest shade
sensitivity = 0/1. ‡Values within a column followed by the same letter are not significantly
different at P≤0.05 by protected LSD. §Values within a row followed by the same letter are not significantly different
at P≤0.05 by protected LSD.
biomass, and root length in 64% shade, the best cultivars were Celebration, TiftNo.4,
TiftNo.1, and Transcontinental (Table 4.5). Cultivars with intermediate shade tolerance
included Aussie Green, MS-Choice, Princess 77, SWI-1045, SWI-1041, and SWI-1012.
Most shade sensitive cultivars were SWI-1014, Arizona Common, Sundevil, SR 9554,
GN-1, and Patriot.
The top ranked cultivar across all parameters was Celebration (Table 4.5). When
grown in shade, Celebration was able to consistently maintain TQ, chlorophyll, root
length, and root biomass in the top statistical category. In a previous investigation,
Celebration was noted for its relative shade-tolerance (Bunnell et al., 2005c). At 71%
shade, Celebration and „Meyer‟ zoysiagrass maintained similar TQ scores at a 25 mm
mowing height, while Tifway and TifSport were deemed commercially unacceptable. In
this study, Celebration had TQ scores of 6.5 and 4.5 at weeks 4 and 8, respectively, while
Tifway and TifSport TQ scores were consistently lower throughout the duration of the
74
Table 4.5. Overall shade tolerance rank of 42 bermudagrass cultivars after 8
weeks of full-sunlight (control) and 64% continuous shade at the Clemson
University research greenhouse complex.
Cultivar Rank† Cultivar Rank
Celebration 6 Mohawk 1
TiftNo.4 5 SWI-1001 1
TiftNo.1 5 Tifway 1
Transcontinental 5 Midlawn 1
SWI-1003 4 Tifsport 1
Sunbird 4 OR 2002 1
Aussie Green 3 Ashmore 1
MS-Choice 3 CIS-CD5 1
Princess 77 3 CIS-CD6 1
SWI-1045 3 CIS-CD7 1
SWI-1041 3 Panama 1
SWI-1012 3 La Paloma 1
B-14 2 Yukon 1
Riviera 2 OKC 70-18 1
SWI-1046 2 NuMex Sahara 1
TiftNo.3 2 SWI-1014 0
Southern Star 2 GN-1 0
TiftNo.2 2 Patriot 0
Sunstar 1 Sundevil 0
SWI-1044 1 SR 9554 0
FMC-6 1 Arizona Common 0
†Rank indicates number of times a cultivar placed in the top statistical category
when grown under 64% continuous shade. Greatest shade tolerance = 6, greatest
shade sensitivity = 0.
8-week study (Table 4.1). Jiang et al. (2004 and 2005) also noted TifSport bermudagrass
as shade-sensitive when compared to various seashore paspalum cultivars. Gaussoin et
al. (1988) noted Tifway as shade sensitive when compared to 31 other bermudagrass
cultivars.
75
Arizona Common was in the lowest statistical category for all parameters
measured when grown in shade. In another greenhouse shade study, Gaussoin et al.
(1988) regarded Arizona Common as highly shade-intolerant. Similar results in this
study were noted as Arizona Common did not rank in the top statistical category for any
of the measured parameters, indicating relative shade sensitivity.
Conclusion
While relative shade-tolerance of bermudagrass cultivars was examined in this
study, all cultivars had unacceptable TQ scores. Future research should examine the
relatively shade-tolerant and shade-intolerant cultivars to provide insight into the
physiological mechanisms associated with variation in shade response among
bermudagrass cultivars.
76
CHAPTER V
DORMANT BERMUDAGRASS SPRING GREEN-UP INFLUENCED BY SHADE
Introduction
Bermudagrass (Cynodon spp.) is the predominant turfgrass in warm climatic
regions of the world. However, when temperatures drop below 10oC, bermudagrass
becomes dormant. Due to this, managing bermudagrass in the transition zone is
challenging because of the relatively short growing season of bermudagrass. One major
challenge facing turfgrass managers is bermudagrass spring transition in the transition
zone. The potential of experimental and commercially available bermudagrass cultivars
ability to break dormancy earlier in the spring would greatly benefit many turfgrass
managers. Bermudagrass cultivars with earlier spring green-up (SGU) would benefit the
industry by providing use of sports fields and/or golf courses earlier in the year for
competition, earlier harvest times for sod producers, and perhaps eliminating overseeding
at certain sites.
Another limiting factor for bermudagrass growth and development occurs when
shade persists. Bermudagrass shade intolerance results from its inability to withstand low
light conditions because of its unique photosynthetic pathway (Sage and McKown, 2006;
Horton and Neufeld, 1998) and origin from hot, dry, and sub-humid regions of Africa
(McCarty et al., 2005). Typical responses of bermudagrass grown under shade include a
decrease in density (Jiang et al. 2004; Bunnell et al., 2005a, b; Miller et al., 2005), a
reduction in chlorophyll (Jiang et al. 2004; Bunnell et al., 2005a, b; Baldwin et al., 2008),
77
root mass (Baldwin et al., 2008) and carbohydrate production (Bunnell et al., 2005a, b,
c), decreased canopy photosynthetic rates (Jiang et al. 2004) and reduced antioxidant
enzyme activity (Jiang et al., 2005) and total soluble protein (Jiang et al., 2005)
production.
There have been several recent published reports attempting to either prolong
bermudagrass fall color or encourage bermudagrass breaking dormancy earlier through
the use of cultural practices, such as appropriate fertility (Richardson, 2002; Gilbert and
Kopec, 2004; Bruneau et al., 2004; Munshaw et al., 2006), plant growth regulator
(Fagerness and Yelverton, 2000 and Fagerness et al., 2002 and), colorant (Gilbert and
Kopec, 2004; Long et al., 2005; Liu et al., 2007), and temporary cover (Goatley et al.,
2005 and Goatley et al., 2007) use. To date, no study has evaluated bermudagrass
cultivars transition from winter dormancy into spring when shade is a growth limiting
factor. Also, several experimental and new commercially available bermudagrass
cultivars show improved shade tolerance compared to industry standards (Baldwin et al.,
2008; Hanna and Maw, 2007; Bunnell et al., 2005c). This study will aid turfgrass
managers in cultivar selection when establishing/renovating a tee-box or fairway when
shading is prevalent. Also, this project will benefit sod producers by identifying
bermudagrass cultivars ability to break dormancy earlier in the spring season allowing for
earlier harvest times. Finally, this research project will address how a shaded
microenvironment impacts bermudagrass cultivar SGU. Therefore, a research objective
was to evaluate bermudagrass cultivars SGU when shade is a growth limiting factor and
monitor bermudagrass summer performance following late winter and spring shade.
78
Materials and Methods
Research was conducted at the Turfgrass Research Center, Clemson University,
Clemson, SC from 2 March to 31 July 2006 and repeated in 2007. Bermudagrass
cultivars, „Tifway‟, „Tift No.4‟, „Celebration‟, „Princess 77‟, „Riviera‟, and „Yukon‟
(Table A.1), were maintained in lysimeters 40.64 cm in height and 15.24 cm in diameter
filled with 40.64 cm of 85:15 sand:peat and 10.16 cm gravel (8 to 10 mm in diameter) to
facilitate drainage. Plugs of dormant bermudagrass sod were collected from the 2002
bermudagrass NTEP trials at the Clemson University Research Center and washed free of
soil with roots clipped directly below the thatch layer. Lysimeters were maintained
adjacent to field research plots to mimic natural climatic field conditions (Illustration
D.9). Treatments included a control (full-sunlight) and 55% continuous shade using a
neutral density, polyfiber black shade cloth (Glenn Harp and Sons, Inc., Tucker, GA)
initiating light to moderate shade stress. Shade structures were metal frames with
individual cells measuring 304.8 cm in width, height, and length. Shade cloths supported
by metal frames were placed on top of the structure and extended 182.9 cm down each
side to prevent any morning or evening sunlight encroachment, yet also maintain
adequate air movement. Lysimeters were 81 cm above the ground and ~127 cm away
from each side of the shade material. Also, lysimeters were 227 cm below the top of the
shading material.
Weekly fertilization began 24 April 2006 and 10 April 2007 and ended 31 July
2006 and 2007 using a combination of 10N-1.3P-4.2K and 5N-0P-5.8K liquid fertilizers
79
(Progressive Turf, LLC., Ball Ground, GA) providing nitrogen at a rate of 9.7 kg ha-1
.
For overseeded treatments, fertilization was initiated 1-week following potting. Rates
and methods are similar as described above. A CO2-pressurized backpack sprayer was
used to apply all fertilizers. No fungicides and herbicides were applied as disease and
weed pressure were minimal. Lysimeters were watered daily (if necessary) to prevent
wilt, while mowing occurred every other day at 1.3 cm using a 7.2 volt cordless shear
(model #ssc1000, Black and Decker, Towson, MD).
Data collection
Data collection included visual SGU ratings, visual turfgrass quality (TQ), total
shoot chlorophyll concentration, and root total non-structural carbohydrates (TNC).
Spring green-up was visually recorded every 3- to 4-days once green tissue emerged
using a scale of 0 -100% with 0% = complete brown turfgrass and 100% = complete
green turfgrass.
Visual TQ scores were rated every 2-weeks from 1 June to 31 July, 2006 and
2007. Turfgrass quality ratings were based on color, density, texture, and uniformity of
the bermudagrass surface and rated from 1 to 9, 1 = brown, dead turfgrass, 7 = minimal
acceptable turfgrass, 9 = perfect green, healthy turfgrass.
Total shoot chlorophyll (mg g-1
) was measured end of May and mid-July for both
years. Fresh clippings (minimum 0.1g) were collected from each lysimeter using scissors
and placed in a plastic bag inside a covered bucket to prevent sunlight degradation.
Clippings were weighed (0.1g) and placed in a glass test tube (1.0 cm in width and 14.8
cm in length) with 10 mL of dimethyl sulfoxide (DMSO), which eliminates shoot tissue
80
grinding for chlorophyll extraction (Hiscox and Israelstam, 1979). Samples were
incubated in 65 oC water on a hot plate (PC-600, Corning, Corning, NY) for 1.5-hours
and continuously shaken. Upon completion, samples were passed through filter paper
(Whatman 41, Whatman, England) and remaining extract (2 mL) transferred into
cuvettes. Absorbance values were recorded at 663 nm and 645 nm wavelengths using a
spectrophotometer (GenesysTM
20, ThermoSpectronic, Rochester, NY). Blanks were
initially run and also after every sixth sample. The following formula was used to
calculate total shoot chlorophyll: (mg g-1
) = (8.02 * D663 + 20.2 * D645) * 0.1 (Arnon,
1949).
Root TNC (mg g-1
) was analyzed end of July for both years. Root tissue was
harvested using a bulk density sampler which extracted 154.4 cm3 (10.2 cm in depth)
cores prior to sunrise to minimize any diurnal fluctuations. Following soil removal, root
tissue samples were stored at -75oC until freeze dried at -40
oC for 1-week to cease all
metabolic activity. Samples were then ground using an A-10 plant grinder (IKA Works,
Inc., Wilmington, NC). Grounded samples were rehydrated with 100 L of 80% ethanol
(EtOH) and 2 mL of 0.1 M sodium acetate buffer (pH 4.5) in glass test tubes 13 X 100
mm. Rehydrated samples were placed in boiling water for 1-hour, cooled for 1-hour and
repeated. Then, 2 mL of invertase (Sigma I-4753, 433 units mg-1
) and amyloglucosidase
(Sigma A-7255, 23,000 units g-1
) were added to solution. Samples were placed in a water
bath (40 – 45oC) for 3-days and vortexed three times daily. TNC analysis was analyzed
using Nelson‟s Assay (1944), which determines glucose and fructose in plant tissue
(Nelson, 1944; Somogyi, 1945).A 25 L of aliquot was removed and two reagents
81
(copper and arseno-molybdate) were added to solution. Absorbance values were
measured at 520 nm using a spectrophotometer.
Data Analysis
Treatments were arranged in a randomized complete block design with three
replications. Treatment effects were evaluated using analysis of variance within SAS
(version 9.1, SAS Institute, Cary, NC). Most SGU ratings showed significant year by
treatment interactions, therefore, data from both years are presented separately.
However, TQ, chlorophyll, and root TNC showed no year by treatment interaction, so
data are pooled for both years. Means separation was analyzed using Fisher‟s least
significant difference (LSD) test at P ≥ 0.05.
Results
Spring Green-Up
In year II, SGU was quicker than in year I, which likely led to a significant year
by treatment interaction. It appears greater soil moisture due to rainfall early in the
spring, not air temperature, may have been a significant factor influencing yearly SGU
results. In March, as cultivars began breaking dormancy, year II had 4.4 cm greater
rainfall than year I (Figure 5.1). Average monthly maximum and minimum temperature
differences between year I and II were minimal (Figure 5.2).
Year I
Overall, 55% continuous shade had minimal impacts on SGU ratings in year I
(Table 5.1). On 4 of the 6 rating dates, Princess 77 had ~92% SGU reduction when
82
Figure 5.1. Monthly precipitation (cm) from 2 March to 31 May 2006 and 2007
and historical averages in Clemson, SC.
Figure 5.2. Average monthly maximum and minimum temperatures (oC) from 2 March to
31 May 2006 and 2007 and historical averages in Clemson, SC.
4.78
10.34 10.269.22
2.77
3.76
13.44
9.3710.69
0
2
4
6
8
10
12
14
16
March April May
2006
2007
Historical average
25 25 26
12 12 14
23 23
27
9 10
15
22 22
26
7 8
13
0
5
10
15
20
25
30
March Apri May March April May
o C
2006 2007 Historical average
Maximum Temperature Minimum Temperature
83
Table 5.1. Spring green-up of six bermudagrass cultivars influenced by various light regimes
(full-sunlight and 55% continuous shade) in spring, 2006.
Spring green-up†
--------24 April------ -----------28 April-------- ----------3 May--------- Bermudagrass
cultivar Sun Shade LSD Sun Shade LSD Sun Shade LSD
TiftNo.4 36.7 60.0 NS 35.0 61.7 NS 58.3 66.7 NS
Tifway 36.7 48.3 NS 45.0 30.0 NS 53.3 53.3 NS
Yukon 26.7 33.3 NS 28.3 40.0 NS 46.7 65.0 NS
Celebration 13.3 26.7 NS 11.7 21.7 NS 21.7 40.0 NS
Riviera 6.3 6.7 NS 5.0 11.7 NS 10.0 13.3 NS
Princess 77 16.7 6.7 NS 18.3 10.0 NS 21.6 8.3 13.09§
LSD NS NS 18.87‡ 34.26 NS 44.08
§
Spring green-up†
--------11 May------ ----------19 May-------- -----------5 June------- Sun Shade LSD Sun Shade LSD Sun Shade LSD
TiftNo.4 63.3 76.7 NS 70.0 73.3 NS 90.0 90.0 NS
Tifway 61.7 46.7 NS 88.3 66.7 NS 88.3 80.0 NS
Yukon 53.3 48.3 NS 60.0 61.7 NS 88.3 76.7 NS
Celebration 38.3 45.0 NS 65.0 60.0 NS 93.3 85.0 NS
Riviera 21.7 26.7 NS 41.7 33.3 6.54§ 80.0 60.0 NS
Princess 77 31.7 16.7 6.54§ 53.3 33.3 10.35 80.0 51.7 14.63
§
LSD NS 35.33‡ 22.97
‡ NS NS 19.10
‡
†Spring green-up based on a scale of 0-100%, 0% = complete brown turfgrass, 100% =
complete green turfgrass.
‡Values within a column for each rating date followed by the same letter are not significantly
different at P≤0.05 by protected LSD. §Values within a row for each rating date followed by the same letter are not significantly different
at P≤0.05 by protected LSD. LSD = least significant difference, NS = not significant.
grown in shade compared to full-sunlight treatment. Also, Riviera grown in shade had a
25% SGU delay compared to full-sunlight treatment on 19 May.
Under full-sunlight, cultivars SGU by end of May was >80% (Table 5.1). When
bermudagrass cultivars were grown under shade, SGU varied. On 28 April, TiftNo.4 had
a ~3.8 unit SGU increase compared to Celebration, Riviera, and Princess 77. Similarly,
TiftNo.4 increased SGU by ~5.5 and ~2.7 units compared to Riviera and Princess 77 on 3
84
May and 11 May, respectively. By the end of the spring, Princess 77 showed ~60%
greater SGU delay compared to other cultivars.
Year II
In year II, shade-grown Celebration and TiftNo.4 were the only cultivars not to
show significant SGU delays on any rating date compared to full-sunlight treatments
(Table 5.2). Throughout spring, all other cultivars showed significant SGU delays on 2
or more rating dates. On 29 March, shade-grown Tifway and Yukon had 2.5 and 1.2 unit
SGU decrease, respectively, while on 2 April, shade-grown Tifway and Riviera had 0.9
and 1.6 unit SGU decrease, respectively, compared to sun-grown counterparts. Cultivars
SGU were all reduced on 17 April due to unseasonable cold temperatures the preceding
week. Low temperatures from 7 - 12 April averaged below 0oC. However, no freezing
damage was noted as all cultivars recovered when temperatures the following week
reached 27oC. By 9 May, shade-grown Yukon and Riviera had 11% and 50% reduced
SGU, respectively, compared to full-sunlight treatment.
In the absence of shade, few cultivar SGU ratings differences were noted (Table
5.2). On 17 April 2007, Celebration had a 2.2 and 1.3 unit SGU decrease than TiftNo.4
and Yukon, respectively, when grown in full-sunlight. However, all cultivars, when
grown in full-sunlight, were near 100% green by beginning of May. Cultivars SGU
ratings significantly varied when grown under shade. On 2 April, TiftNo.4 and
Celebration had ~0.9 and ~1.1 unit SGU increase compared to Tifway, Riviera, and
Princess 77. TiftNo.4 had ~56% greater SGU on 24 April than Tifway, Riviera, and
85
Table 5.2. Spring green-up of six bermudagrass cultivars influenced by various light regimes
(full-sunlight and 55% continuous shade) in spring, 2007.
Spring green-up†
---------26 March------ --------29 March------- -------2 April------- Bermudagrass
cultivar Sun Shade LSD Sun Shade LSD Sun Shade LSD
TiftNo.4 28.3 21.7 NS 46.7 46.7 NS 76.7 65.0 NS
Tifway 13.3 10.0 NS 35.0 10.0 13.91§ 65.0 35.0 29.98
§
Yukon 21.6 6.7 13.08§ 63.3 28.3 30.69 73.3 46.7 NS
Celebration 20.0 20.0 NS 43.3 46.7 NS 58.3 70.0 NS
Riviera 30.0 10.0 NS 50.0 26.7 NS 73.3 28.3 35.54
Princess 77 11.7 11.7 NS 25.0 23.3 NS 46.7 38.3 NS LSD NS NS NS 21.69
‡ NS 26.44‡
Spring green-up†
---------17 April-------- ---------24 April------- --------9 May---------
Sun Shade LSD Sun Shade LSD Sun Shade LSD
TiftNo.4 31.7 48.3 NS 91.7 90.0 NS 98.3 98.3 NS
Tifway 16.7 25.0 NS 83.3 60.0 16.68§ 93.3 70.0 NS
Yukon 23.3 31.7 NS 88.3 73.3 NS 98.3 88.3 6.54§
Celebration 10.0 31.7 4.63§ 76.7 71.7 NS 95.0 90.0 NS
Riviera 15.0 11.7 NS 86.7 53.3 20.69 90.0 60.0 26.58
Princess 77 13.3 11.7 NS 85.0 60.0 17.9 93.3 91.7 NS LSD 12.23
‡ 20.76 NS 21.58‡ NS 14.97
‡ †Spring green-up based on a scale of 0-100%, 0% = complete brown turfgrass,
100% = complete green turfgrass. ‡Values within a column for each rating date followed by the same letter are not significantly
different at P≤0.05 by protected LSD. §Values within a row for each rating date followed by the same letter are not significantly different at
P≤0.05 by protected LSD. LSD = least significant difference, NS = not significant.
Princess 77. By 9 May, Riviera and Tifway had ~54% and ~32% greater SGU delay than
TiftNo.4, Yukon, Celebration, and Princess 77.
Turfgrass Quality
Celebration did not show a significant TQ decline throughout summer when
grown under 55% continuous shade (Table 5.3). Compared to full-sunlight, TiftNo.4 had
86
a TQ decline on one rating date, Princess 77 on four rating dates, while Tifway, Yukon,
and Riviera had a TQ decline on all rating dates from 1 June to 31 July when grown
under shade. Compared to full-sunlight, Tifway had the greatest TQ decline (2.5 units),
followed by Yukon (2.2 units), Riviera (1.8 units), Princess 77 (1.5 units), and TiftNo.4
(1.4 units) when grown under shade by 31 July (Illustration D.10).
Sun-grown cultivars showed few significant TQ differences throughout the
summer (Table 5.3). By 31 July, all cultivars TQ were above minimal acceptable
threshold of 7. Bermudagrass cultivar differences when grown under shade occurred on
all rating dates. On 15 June, TiftNo.4 (7.2) and Celebration (6.8) maintained greater TQ
compared to other cultivars when grown under shade, however, Tifway (6.2), Riviera
(5.8), Yukon (5.8), and Princess 77 (5.5) performed similarly. TiftNo.4 and Celebration
show ~1.7 and ~1.3 unit TQ increase, respectively, compared to other cultivars during
July. At the end of July, Princess 77 (5.8) had higher TQ scores than Yukon (5.0), while
Tifway and Riviera had same TQ score of 5.5. By 31 July, regardless of a cultivars
performance under shade, all cultivars TQ was below the minimal acceptable threshold of
7.
Chlorophyll and root total non-structural carbohydrates
In May, cultivars grown under shade had chlorophyll increases compared to full-
sunlight grown cultivars (Table 5.4). Only Princess 77 and Yukon chlorophyll
concentration remain unchanged in May, while other shade-grown cultivars increased
chlorophyll ~26% compared to full-sunlight. In July, shade-grown TiftNo.4 and
87
Table 5.3. Turfgrass quality of six bermudagrass cultivars influenced by various light
regimes (full-sunlight and 55% continuous shade) from 1 June to 31 July, 2006 and 2007.
Turfgrass quality†
---------1 June------- --------15 June--------- ------1 July------ Bermudagrass
cultivar Sun Shade LSD Sun Shade LSD Sun Shade LSD TiftNo.4 7.5 7.2 NS 7.7 7.2 NS 7.5 7.5 NS
Tifway 7.5 5.8 1.49§ 7.2 5.7 1.09
§ 7.5 6.2 1.33
§
Yukon 6.8 6.0 0.67 7.0 5.7 0.54 7.0 5.8 0.67
Celebration 7.3 6.8 NS 7.2 6.8 NS 7.5 7.0 NS
Riviera 6.8 5.8 0.86 7.0 5.2 0.77 6.8 5.8 0.54
Princess 77 6.5 5.8 NS 6.8 5.7 0.67 6.7 5.5 0.77
LSD NS 0.79‡ NS 0.69
‡ NS 0.74
‡
Turfgrass quality†
----------15 July------- ------31 July-------
Sun Shade LSD Sun Shade LSD
TiftNo.4 7.5 7.7 NS 8.2 6.8 0.86§
Tifway 7.5 6.2 1.15§ 8.0 5.5 0.67
Yukon 7.0 5.5 0.77 7.2 5.0 0.67
Celebration 7.7 7.0 NS 7.7 6.7 NS
Riviera 7.0 5.5 0.86 7.3 5.5 1.02
Princess 77 6.8 5.3 0.67 7.3 5.8 0.54
LSD NS 0.77‡ 0.72
‡ 0.74
†Turfgrass quality based on a scale of 1-9, 1=brown/dead turfgrass, 7=minimally acceptable
turfgrass, 9=healthy/green turfgrass. ‡Values within a column for each rating date followed by the same letter are not significantly
different at P≤0.05 by protected LSD. §Values within a row for each rating date followed by the same letter are not significantly
different at P≤0.05 by protected LSD. LSD = least significant difference, NS = not significant.
88
Table 5.4. Chlorophyll concentration (mg g-1
) and root total non-structural
carbohydrates (TNC) (mg g-1
) of six bermudagrass cultivars influenced by various
light regimes (full-sunlight and 55% continuous shade) in July, 2006 and 2007.
Chlorophyll (mg g-1
)
-----------------May-------------------- -----------------July--------------- Bermudagrass
cultivar Sun Shade LSD Sun Shade LSD
TiftNo.4 1.80 2.23 0.40‡ 2.07 2.61 0.49
‡
Tifway 1.78 2.26 0.30 2.30 2.38 NS
Yukon 1.74 1.96 NS 2.24 2.31 NS
Celebration 2.27 2.71 0.34 2.53 2.89 0.27
Riviera 1.78 2.35 0.39 2.23 1.94 NS
Princess 77 1.99 2.18 NS 2.18 2.32 NS LSD 0.33
† 0.41 NS 0.43†
TNC (mg g-1
)
------------------July-------------------
Sun Shade LSD
TiftNo.4y 40.1 36.9 NS
Tifway 33.6 31.7 1.34‡
Yukon 35.6 34.9 NS Celebration 37.3 34.7 NS Riviera 36.3 34.2 NS Princess 77 36.7 40.7 NS LSD NS NS †Values within a column for each rating date followed by the same letter are not
significantly different at P≤0.05 by protected LSD. ‡Values within a row for each rating date followed by the same letter are not significantly
different at P≤0.05 by protected LSD. LSD = least significant difference, NS = not significant.
Celebration increased chlorophyll 26% and 14% compared to sun-grown counterparts,
while chlorophyll concentration for other cultivars was not impacted by shade. Root
TNC were minimally impacted by full-sunlight or shade, however, Tifway had a 6% root
TNC decrease in shade compared to full-sunlight.
89
Discussion
Under moderate shade stress, bermudagrass cultivars maintained at fairway height
standards showed minimal negative impacts when transitioning from winter dormancy
into spring. Minimal cultivar differences could have been associated with fertility and
the microenvironment created by shade. Typically, most golf course fairways, sports
fields, and/or home lawns are fertilized with a granular fertilizer at a high rate in the
spring to promote green leaf tissue emergence. However, in this study, cultivars were
supplied with 9.7 kg ha-1
of N weekly using foliar products to ensure uniform coverage.
Therefore, a rapid flush of growth did not occur which may be more representative of a
field environment. Due to slowed growth from low and frequent N rates/applications
(i.e., spoon feeding), excessive tissue removal did not occur, which is typically
detrimental for warm-season turfgrass growth under shade (Beard, 1997). Shade alters a
microenvironment by extending dew durations (Dudeck and Peacock, 1992) and reducing
evapotranspiration (ET) rates (Beard, 1973). While not measured in this study, dew
duration (visual assessment) of cultivars in shade was generally longer than in full-
sunlight. Also, plants may have had access to greater water in the soil due to reduced
water demand of turfgrass grown under shade. Soil moisture is a critical factor for
successful bermudagrass spring transition (McCarty, 2005c). Future studies monitoring
soil water content under shade and evaluating water-use characteristics of turfgrasses
under shade would prove beneficial.
Cultivars SGU least impacted by shade were TiftNo.4 and Celebration, while
Riviera and Tifway showed greatest SGU decline when grown in shade. Previous
90
investigations have also noted these cultivars for relative shade tolerance and sensitivity
compared to bermudagrass industry standards (Gaussoin, 1988; Bunnell et al., 2005c;
Hanna and Maw, 2007; Baldwin et al., 2008). Also, Celebration and TiftNo.4 were able
to maintain near acceptable TQ scores under 55% continuous shade compared to other
cultivars in the summer. Reasons why these cultivars are relatively shade-tolerant
compared to industry standards largely remains unclear. The relatively shade-
tolerantbermudagrasses may more effectively utilize sunflecks (Sage and McKown,
2006) or maintain a more horizontal growth habit (minimizing excessive tissue removal)
under shade due to plant hormone manipulation. Future anatomical, morphological, and
physiological studies comparing relatively shade-tolerant and sensitive bermudagrass
cultivars would provide insight into why Celebration and TiftNo.4 are superior compared
to industry standards when grown under shade.
Few SGU differences were noted among sun-grown cultivars in both years.
Munshaw et al. (2006) reported Riviera had greater SGU than Tifway and Princess 77,
however, this study was conducted in Blackburg, VA with air temperatures reaching well
below 0oC. It appears the relative cold tolerance of these cultivars probably played a
factor in their SGU performance. Anderson et al. (2007) noted Riviera as a relatively
freeze-tolerant seeded bermudagrass cultivar, while Tifway possessed intermediate cold-
tolerance among vegetative cultivars. Cold-tolerance of these bermudagrass cultivars
was not a factor in this study since air temperatures never reached lethal temperatures of -
5oC to
-12.2
oC (McCarty et al., 2005).
91
Chlorophyll concentrations for several cultivars in May and July increased in
shade compared to full-sunlight. Jiang and Huang (2001) noted chlorophyll increases in
cool-season turfgrasses subjected to an environmental stress. Miller et al. (2005) also
noted minimal reductions in chlorophyll concentrations for „Tifdwarf‟ and „Floradwarf‟
bermudagrass grown under a variety of shaded environments. Bermudagrass decline in
shade is often attributed to reduced lateral stem growth (Beard, 1997), while the
formation of thin, etiolated leaves decreases plant density. Plants grown in shade
typically have larger and fewer chloroplasts than sun-grown plants, thus more chlorophyll
concentrations in individual leaves are noted in shade-grown plants (Boardman, 1977).
Therefore, in this study, while density decreased (i.e., low TQ scores) for bermudagrass
cultivars grown under shade, chlorophyll concentrations of green leaf tissue collected for
chlorophyll analysis (0.1 g of fresh clipping weight) may have possessed greater
chlorophyll due to chloroplast size. Future studies investigating chloroplast development
of shaded bermudagrasses would provide insight into the previous statement.
Conclusion
While TiftNo.4 and Celebration had highest TQ scores throughout the summer,
both cultivars TQ was below acceptable standards by 31 July. However, these cultivars,
as well as other cultivars selected in this study, performance would be improved by plant
growth regulator use (Qian et al., 1998; Qian and Engelke, 1999; Bunnell et al., 2005b;),
minimizing N application rates (Burton et al., 1959; Bunnell et al., 2005b;), mowing
height increases (White, 2004; Bunnell et al., 2005b;), and appropriate water
92
management (Dudeck and Peacock, 1992). In summary, compared to full-sunlight,
TiftNo.4 and Celebration SGU were least affected by shade, Tifway and Yukon SGU
were intermediately reduced by shade, and Riviera and Princess 77 showed greatest SGU
delays when grown under shade.
93
CHAPTER VI
WINTER CULTURAL PRACTICES AND SHADE IMPACTS ON „TIFEAGLE‟
BERMUDAGRASS SPRING GREEN-UP
Introduction
Spring green-up (SGU) is defined as the initial seasonal appearance of green
shoots as spring temperature and moisture conditions become favorable, thus breaking
winter dormancy (Beard, 2005). Delay of SGU often leaves bermudagrass weak with
large bare areas. Spring green-up is often delayed by winter overseeding (Mazur and
Rice, 1999; Horgan and Yelverton, 2001; Liu et al., 2007). In the transition zone,
turfgrass managers are faced with the yearly decision of whether or not to overseed
bermudagrass putting greens to provide financially important winter green color. The
practice of overseeding is detrimental as both species compete for the same resources:
water, nutrients, and sunlight. Also, trees successfully out-compete turfgrasses for these
same essential resources. Previous research has indicated all major bermudagrass putting
green cultivars are sensitive to low light environments (Miller and Edenfield, 2002;
Bunnell et al., 2005a and b; Miller et al., 2005).
Year-round golf course use, increased television coverage of tournaments, and
meeting player expectations often preclude the option of simply leaving brown, dormant
bermudagrass during winter. Traditionally, overseeding bermudagrass with a cool-
season turfgrass has been the most widely used option for a turfgrass manager to provide
acceptable winter color. An alternative gaining popularity to alleviate overseeding and
94
difficult spring transition, is use of turfgrass colorants or dyes (Machi, 2007). Turfgrass
colorant use began in the mid-1950‟s (Kurtz, 2003); however, only a few scientific
reports investigating colorant use as an alternative to overseeding were published
(Younger and Fucbigami, 1958; Van Dam and Kurtz, 1971; Henry and Gibeault, 1985).
Recently, Shearman et al. (2005) noted a turfgrass colorant improved buffalograss
(Buchloe dactyloides [Nutt.] Engelm.) quality and color ratings and also enhanced SGU.
Gilbert and Kopec (2004) also indicated turfgrass colorants enhanced SGU of dormant
„Tifway‟ bermudagrass (Cynodon dactylon). Long et al. (2005) reported colorant use on
a „Champion‟ bermudagrass putting green was a safe and suitable alternative to
overseeding for winter color and playability. Similarly, Liu et al. (2007) indicated
colorants used on a „TifEagle‟ bermudagrass putting green provided comparable winter
color to overseeded bermudagrass. Other advantages of using colorants include cost
reductions. The cost of overseeding is estimated from $500 to over $2000 per acre
(McCarty, 2005), while using colorants reduces this expense by approximately one-half
(Carson, 2004; Van Dam, 1972).
Our objective for this research was to determine the impacts of different cultural
practices (overseed, colorant use, and dormant turfgrass) and shade on TifEagle
bermudagrass spring transition and summer performance.
95
Materials and Methods
A two-year research project was conducted at the Turfgrass Research Center,
Clemson University, Clemson, SC on TifEagle bermudagrass maintained in lysimeters
40.64 cm in height and 15.24 cm in diameter filled with 30.50 cm of 85:15 sand:peat and
10.16 cm gravel (8 to 10 mm in diameter) to facilitate drainage. A TifEagle
bermudagrass research green was treated with Titan colorant (Burnett Lime Co.,
Campobello, SC) at 2.4 L 100 m-2
first week of December and re-treated first week of
February at the same rate for both years. Also, the TifEagle research green was
overseeded first week of October with Poa trivialis (L.) at a rate of 390 kg pure live seed
ha-1
following standard preparatory steps for overseeding (McCarty, 2005). Plugs of
untreated, overseeded, and colorant-treated TifEagle bermudagrass sod were collected on
8 March 2006 and 15 March 2007 and washed free of soil with roots clipped directly
below the thatch layer prior to treatment initiation. Lysimeters were maintained adjacent
to field research plots to mimic natural climatic field conditions. Shade levels included a
control (full-sunlight) and 55% continuous shade using a neutral density, polyfiber black
shade cloth (Glenn Harp and Sons, Inc., Tucker, GA) initiating moderate shade stress.
Shade structures were metal frames with individual cells measuring 305 cm in width,
height, and length. Shade cloth extended 183 cm down each lysimeter side to prevent
morning or evening sunlight encroachment, and 227 cm below the shade material to
allow adequate air movement. Lysimeters were 81 cm above the ground and ~127 cm
centered from each side of the shade material.
96
Weekly fertilization began 24 April 2006 and 10 April 2007, ending 31 July 2006
and 2007, using a combination of 10N-1.3P-4.2K and 5N-0P-5.8K liquid fertilizers
(Progressive Turf, LLC., Ball Ground, GA) which provided nitrogen (N) at a rate 9.7 kg
ha-1
. For overseed treatments, fertilization was initiated one-week following potting. A
CO2-pressurized backpack sprayer calibrated at 108 gal ac-1
(1010 L ha-1
) was used to
apply all fertility. No fungicides or herbicides were needed. Lysimeters were watered as
needed to prevent wilt and mowed daily at 0.3 cm using handheld 7.2 volt cordless shear
(model #ssc1000, Black and Decker, Towson, MD) with clippings removed.
Data collection
Data collection included SGU, visual turfgrass quality (TQ) ratings, total shoot
chlorophyll, and root total nonstructural carbohydrates (TNC). Spring green-up was
visually estimated every seven to ten days once green tissue emerged using a scale of 0 -
100% with 0% = complete brown bermudagrass and 100% = complete green
bermudagrass. Bermudagrass and P. trivialis were visually separated due to morphology
differences.
Visual TQ scores were rated every two weeks from 1 June to 1 August, 2006 and
2007. Turfgrass quality ratings were based on color, density, texture, and uniformity of
the bermudagrass surface and rated from 1 to 9, 1 = brown, dead turfgrass, 7 = minimal
acceptable turfgrass, 9 = perfect green, healthy turfgrass.
Total shoot chlorophyll (mg g-1
) was measured end of May and mid-July for both
years. Fresh clippings of bermudagrass were collected from each lysimeter and placed in
a plastic bag inside a covered bucket to prevent sunlight degradation. Clippings were
97
weighed (0.1g) and placed in a glass test tube (1.0 cm in width and 14.8 cm in length)
with 10 mL of dimethyl sulfoxide (DMSO), which eliminates shoot tissue grinding to
extract chlorophyll (Hiscox and Israelstam, 1979). Samples were incubated in 65 oC
water on a hot plate (PC-600, Corning, Corning, NY) for 1.5 hr and continuously shaken.
Upon completion, remaining extract (2 mL) was transferred into cuvettes. Absorbance
values were recorded at 663 nm and 645 nm wavelengths using a spectrophotometer
(GenesysTM
20, ThermoSpectronic, Rochester, NY). Blanks were initially run and after
every sixth sample. The following formula was used to calculate total shoot chlorophyll:
(mg g-1
) = (8.02 * D663 + 20.2 * D645) * 0.1 (Arnon, 1949).
Root TNC (mg g-1
) was analyzed end of July for both years. Root tissue was
harvested using a bulk density sampler which extracted 154.4 cm3 (10.2 cm in depth)
cores prior to sunrise to minimize any diurnal fluctuations. Following soil removal, root
tissue samples were stored at -75oC until freeze dried at -40
oC for one week to cease all
metabolic activity. Samples were then ground using an A-10 plant grinder (IKA Works,
Inc., Wilmington, NC). Grounded samples were rehydrated with 100 L of 80% ethanol
(EtOH) and 2 mL of 0.1 M sodium acetate buffer (pH 4.5) in glass test tubes 13 X 100
mm. Rehydrated samples were placed in boiling water for 1 hr, cooled for 1 hr and
repeated. Then, 2 mL of invertase (Sigma I-4753, 433 units mg-1
) and amyloglucosidase
(Sigma A-7255, 23,000 units g-1
) were added to the solution. Samples were placed in a
water bath (40 – 45oC) for three days and vortexed three times daily. TNC analysis was
analyzed using Nelson‟s Assay (1944), which determines glucose and fructose in plant
tissue (Nelson, 1944; Somogyi, 1945). A 25 L aliquot was removed and two reagents
98
(copper and arsenomolybdate) were added to the solution. Absorbance values were
measured at 520 nm using a spectrophotometer.
Data Analysis
Treatments were arranged in a randomized complete block design with three
replications. Results were analyzed using the Statistical Analysis System (SAS) (version
9.1, SAS Institute, Cary, NC). Spring green-up ratings were recorded on different, but
comparable dates each year due to different spring weather patterns for 2006 and 2007.
No meaningful treatment by year interaction was detected SGU ratings or other response
measures; therefore, data for the two years were combined. Mean separation was
performed using Fisher‟s protected least significant difference (LSD) test with = 0.05.
Results
When grown in full-sunlight, quickest SGU ratings were consistently noted for
colorant use on rating dates 20 March to 15 May (Table 6.1). On the first rating date,
colorant treatment showed a 2.7 and 7.3 unit SGU increase compared to full-sunlight
dormant and overseed treatments. Similar trends continued throughout the spring as
colorant use provided greatest SGU ratings compared to dormant and overseed treatments
in full-sunlight (Illustration D.11). Also, dormant bermudagrass showed ~1.1 unit SGU
increase compared to the overseed treatment from week 2 to week 7 when grown in full-
sunlight. No SGU differences were noted between colorant use and dormant
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Table 6.1. Spring green-up of 'TifEagle' bermudagrass influenced by various winter
cultural practices (colorant, overseed, and dormant) and light intensities (full-
sunlight and 55% continuous shade) recorded from 20 March to 15 May, 2006 and
2007.
-------------------Spring Green-Up (0-100%)†---------------
Light
Treatment
Cultural
Practice Wk 1 Wk 2 Wk 3 Wk 4 Wk 5 Wk 6 Wk 7
Full-
sunlight Colorant 62.5 76.7 76.7 90.0 60.8 87.5 100.0
None 16.7 35.8 42.5 55.8 29.2 68.3 91.7
Overseed 7.5 16.7 25.8 23.3 9.2 31.7 71.7
55%
Shade§ Colorant 29.2 52.5 57.5 65.8 46.7 87.5 100.0
None 16.7 34.2 40.0 44.2 25.0 50.0 93.3
Overseed 2.5 3.3 15.8 16.7 5.0 18.3 51.7
LSD 10.97‡ 10.13 12.56 7.56 7.81 8.18 14.67
†Spring green-up based on a scale of 0-100%, 0% = complete brown turfgrass, 100% =
complete green turfgrass. ‡Values within a column followed by the same letter are not significantly different at
P≤0.05 by protected LSD. §Shade: 55% continuous shade.
LSD = Least significant difference.
bermudagrass by the end of May. When grown in full-sunlight, colorant and dormant
treatments enhanced SGU ~34% compared to the overseed treatment by week 7.
Shade impacted SGU for all treatments on various rating dates (Table 6.1).
Shade-grown colorant-treated TifEagle bermudagrass reduced SGU ~37% from week 2
through week 5 compared to sun-grown colorant treatment. However, colorant treated
TifEagle grown in shade increased SGU ~0.6 and ~7.2 units compared to shade-grown
dormant and overseed treatments from week 1 to week 6, respectively. When
overseeded, shade reduced SGU 4.1, 0.73, and 0.39 units by week 2, 6, and 7,
respectively, compared to the sun-grown overseed treatment (Illustration D.12).
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Table 6.2. Turfgrass quality of 'TifEagle' bermudagrass influenced by various
winter cultural practices (colorant, overseed, and dormant) and light intensities
(full-sunlight and 55% continuous shade) from 1 June to 1 August, 2006 and
2007.
-----------------Turfgrass Quality
†---------------------
Light
Treatment
Cultural
Practice 1 June 15 June 1 July 15 July 1 August
Full-
sunlight Colorant 7.7 7.8 7.3 8.0 8.0
Dormant 6.7 7.3 7.5 7.3 7.8
Overseed 5.2 4.8 6.0 5.8 5.5
55%
Shade§ Colorant 6.3 7.0 7.2 6.8 6.7
Dormant 5.7 6.5 7.3 6.2 6.2
Overseed 4.5 5.0 5.0 5.2 4.3
LSD 0.77‡ 0.66 0.69 0.79 0.72
†Turfgrass quality based on a scale of 1-9, 1=brown/dead turfgrass, 7=minimally
acceptable turfgrass, 9=healthy/green turfgrass. ‡Values within a column followed by the same letter are not significantly different at
P≤0.05 by protected LSD. §Shade: 55% continuous shade.
LSD = Least significant difference.
With the exception of 1 June rating, summer TQ scores remained similar for sun-
grown colorant and dormant treatments (Table 6.2). However, when winter overseeded,
full-sunlight TQ scores were ~2.3 and ~1.9 units lower than colorant and dormant
treatments, respectively, on all summer rating dates. No TQ differences were noted
between shade-grown colorant and dormant treatments from 15 June to 1 August.
Overseeded TifEagle bermudagrass grown under shade had ~2.0 and ~1.7 unit TQ
decrease compared to shade-grown colorant and dormant treatments, respectively, on all
TQ rating dates. By the end of the study, all treatments grown in shade were below
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acceptable threshold of 6 and were significantly reduced compared to their full-sunlight
counterparts. Also, winter overseeded TifEagle TQ never surpassed the acceptable
threshold of 7, regardless of light environment.
Dormant TifEagle bermudagrass grown in shade had a 14% chlorophyll increase
compared to its sun-grown counterpart in May (Table 6.3). Light environment did not
impact chlorophyll concentration of colorant or overseed treatments. In full-sunlight,
colorant treatment had 20% greater chlorophyll than overseed, while in shade, a 50%
chlorophyll increase was noted for colorant treatment compared to the overseed
treatment. No differences were noted for July chlorophyll. In full-sunlight, colorant and
dormant treatments had ~62% greater root TNC than the shaded overseed or shade-grown
dormant treatment. Overseeded TifEagle grown in full-sunlight had a 49% root TNC
increase compared to its shade counterpart. Other cultural practices showed no root TNC
differences between sunlight and shade treatments.
Discussion
Historically, warm-season turfgrass managers provided adequate and acceptable
winter color and cover by overseeding with a cool-season turfgrass, often with spring
transition problems. Our results strongly suggest overseeding a TifEagle bermudagrass
green should be avoided, especially when shade is problematic. The overseeded turfgrass
was persistent and competitive through the end of May. In this study, no cultural or
chemical means were attempted to remove the overseeded turfgrass. Also, Poa trivialis
is considered a relatively shade tolerant species due to its origin in Northern Europe
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Table 6.3. Total shoot chlorophyll (mg g-1
) and root total non-structural
carbohydrates (TNC) (mg g-1
) of 'TifEagle' bermudagrass influenced by various
winter cultural practices (colorant, overseed, and dormant) and light intensities
(full-sunlight and 55% continuous shade) in May and July, 2006 and 2007.
Chlorophyll (mg g
-1)
TNC
(mg g-1
)
Treatment Cultural Practice May July July
Full-sunlight Colorant 2.47 2.88
42.18
Dormant 2.35 3.09
37.81
Overseed 2.06 2.94
37.32
Shade‡ Colorant 2.67 3.00
33.61
Dormant 2.68 2.99
27.09
Overseed 1.78 2.99
25.03
LSD 0.31† NS 11.65
†Values within a column followed by the same letter are not significantly different at
P≤0.05 by protected LSD. ‡Shade: 55% continuous shade.
LSD = Least significant difference.
NS = not significant
(McCarty, 2005). Therefore, overseeding transition may be improved if appropriate
cultural and chemical practices were utilized. Previous research indicates various cultural
and chemical means to remove an overseeded turfgrass has both positive and negative
impacts on bermudagrass spring transition (Mazur and Wagner 1987; Horgan and
Yelverton, 2001; Mitra et al., 2008).
Colorant-treated shade-grown TifEagle bermudagrass showed significantly
greater SGU enhancement compared to sun-grown dormant and overseeded TifEagle
bermudagrass on most rating dates (Table 1). This can be attributed to at least two
factors: soil moisture content and surface/soil temperatures. While these parameters were
103
not measured in this study, Liu et al. (2007), Long et al. (2005), Shearman et al. (2005),
and Gilbert and Kopec (2004) attributed enhanced colorant-treated TifEagle and
Champion bermudagrass, buffalograss, and Tifway bermudagrass SGU to increased soil
or surface temperatures. Also, turfgrasses under shade have lower evapotranspiration
rates and cooler temperatures (Beard, 1973). Soil moisture and temperatures are two
critical factors for adequate bermudagrass spring transition (McCarty, 2005). The
combination of warmer surface/soil temperatures from the colorant and increased soil
water content due to reduced ET under shade contributed to quicker bermudagrass SGU.
The previous statement is beyond the scope of this project, however, future field
evaluations are necessary to determine if colorant use can slightly mitigate bermudagrass
shade stress when transitioning from winter dormancy.
Dormant TifEagle grown in shade showed greater chlorophyll concentration than
full-sunlight dormant treatment. Previous reports have also noted chlorophyll increases
under environmental stresses, such as shade and drought (Jiang and Huang, 2001;
Baldwin et al., 2008). Boardman (1977) indicated shade plant leaves typically have
larger, but fewer chloroplasts that contain greater chlorophyll concentrations than sun-
grown plant leaves. Also, plants grown in shaded environments typically have thinner
and etiolated leaves. In this study, while TifEagle shoot density was visually low in
shade, only a small amount of green tissue (0.1 g) was collected for chlorophyll analysis,
which may have contained a greater amount of chlorophyll than sun-grown treatments.
Therefore, in this study, chlorophyll was a poor indicator of TifEagle bermudagrass TQ
and density when grown in shade.
104
Winter cultural practices and light environment negatively influenced TifEagle
bermudagrass summer root carbohydrate reserves. When overseeded and grown in
shade, TifEagle root TNC was significantly lower compared to most other treatments.
This is probably attributed to root competition and additional light interruptions to
TifEagle provided by Poa trivialis root system and canopy. However, no root TNC
differences among any winter treatments when grown in full-sunlight were noted. Unlike
perennial ryegrass (Lolium perenne L.) cultivars, which possess improved heat and
drought tolerance, Poa trivialis is relatively heat sensitive and in this study, was less
persistent when grown in full-sunlight compared to shade. Root carbohydrate data most
likely indicates that reduced competition from Poa trivialis roots and overhead canopy
existed in full-sunlight, which led to minimal carbohydrate differences for sun-grown
treatments.
Conclusion
Based on this study, along with other recent studies (Gilbert and Kopec, 2004;
Long et al., 2005; Shearman et al., 2005; Liu et al., 2007), it appears colorant use will
become a permanent management practice in the turfgrass industry. While colorant use
seems promising, challenges remaining include educating and easing public
perceptions/concerns about playing on a colorant-treated surface, longevity of colorants,
continued colorant production that mimics natural turfgrass color, colorant application
rates, frequency, and timing, and proper colorant application equipment to achieve
uniformity (i.e., nozzles, sprayer type, nozzle distance from surface, etc…..).
105
CHAPTER VII
MANAGEMENT PRACTICES TO ENHANCE „CHAMPION‟ BERMUDAGRASS
PUTTING GREEN UNDER SHADE
Introduction
Sound agronomic practices are essential for successful turfgrass management.
Three essential turfgrass cultural practices are nutrition, water, and mowing. Appropriate
management of these cultural practices is vital for a healthy, vigorous turfgrass stand,
especially in an unfavorable microenvironment, such as reduced light. Sound agronomic
practices can mask and at times, improve turfgrass response when environmental stresses
exist. When sunlight is limited, appropriate fertility, plant growth regulator (PGR) use,
and mowing practices are critical for successful turfgrass culture.
Nitrogen is perhaps the most dynamic and important nutrient for turfgrasses
because it improves color, density, recuperative ability, and plant health when applied at
adequate rates (Liu et al., 2008). A reduction of nitrogen (N) will enhance a turfgrass
stand when light interception is limited. Burton et al. (1959) reported high N (726 kg ac-
1) in 64% shade decreased „Coastal‟ bermudagrass (Cynodon dactylon L.) carbohydrates
30% and decreased plant density and leaf area compared to low N (90 kg ac-1
). Bunnell
et al. (2005b) also noted a 39% TNC reduction in heavily shaded „TifEagle‟
bermudagrass with additional N (24.5 kg ha-1
(NH4)2SO4). Stanford et al. (2005) noted
„Tifdwarf‟ bermudagrass internode and leaf length significantly increased when
photosynthetic photon flux density (PPFD) was reduced from 975 to 300 mol m-2
s-1
.
106
Also, applications of N at 8.1 kg ha-1
wk-1
significantly reduced leaf length, internode
length, and above ground dry matter of Tifdwarf bermudagrass compared to 24.4 kg N
ha-1
wk-1
(Stanford et al., 2005). Therefore, reduced N rates should enhance turfgrass
performance in shade by reducing above ground vertical growth. Similar trends are also
noted for cool-season turfgrasses grown under shade (Schmidt and Blaser, 1967; Bell and
Danneberger, 1999b; Goss et al., 2002).
Trinexapac-ethyl (TE) has become a routine management practice for turfgrass
managers. Since TE inhibits GA20 to GA1 production, vertical shoot growth is slowed
(Adams et al., 1992). Excessive shoot growth in shade rapidly depletes plant
carbohydrate reserves resulting in turfgrass thinning and TQ decline. Morphological
limitations, such as reduced lateral stem growth inhibit warm-season turfgrass
development when sunlight is blocked (Beard, 1997). Therefore, TE is an effective
management tool to mitigate shade stress because vertical shoot growth is reduced.
„Diamond‟ zoysiagrass (Zoysia matrella (L.) Merr) grown under 86% shade with TE
applied every month at 0.048 kg a.i. ha-1
or every other month at 0.096 kg a.i. ha-1
significantly enhanced turfgrass quality (TQ), root production, root + rhizome tissue
carbohydrates, and photosynthetic efficiency (Qian and Engelke, 1999). Similarly, Qian
et al. (1998) demonstrated TE prolonged Diamond zoysiagrass acceptable TQ (>6) for
134 more days compared to non TE-treated under 88% shade. Also, TE-treated
zoysiagrass had 113% greater TNC and 50% greater canopy photosynthetic rate
compared to non TE-treated (Qian et al., 1998). Bunnell et al. (2005b) noted TifEagle
bermudagrass grown in 4 hours of sunlight showed greater TQ scores and chlorophyll
107
concentration with TE applications (0.0393 kg a.i. ha-1
) every three weeks along with an
increase in mowing height (4.7 mm).
Bermudagrasses have been noted for their poor performance in a shaded
microenvironment. For example, TifEagle bermudagrass requires 32.6 mol m-2
d-1
of
sunlight (Bunnell et al., 2005a), while „Floradwarf‟ and Tifdwarf bermudagrass require
~38.6 mol m-2
d-1
(Miller et al., 2005) of sunlight for an acceptable appearance. Also,
Bunnell et al. (2005c) indicated zoysiagrass was more shade tolerant than bermudagrass,
while Jiang et al. (2004 and 2005) noted seashore paspalum cultivars were more shade
tolerant than selected bermudagrass cultivars. Although bermudagrass performs poorly
in shade, superintendents in the eastern part of the transition zone are considering
switching from predominately bentgrass greens to bermudagrass greens in an attempt to
alleviate bentgrass summer stress management challenges (Hartwiger and O‟Brien,
2006). Bentgrass greens are able to grow under moderate shade because they are adapted
to cool, moist climates (McCarty et al., 2005); however, conversion to bermudagrass
greens will be problematic where moderate shade is present. Unless tree removal is a
viable option, shade will be a constraint for growing ultradwarf bermudagrass.
Therefore, sound management practice recommendations will become more important
enabling superintendents to appropriately manage bermudagrass greens under shade.
Champion bermudagrass is gaining popularity as a golf course putting green,
however, field research of Champion bermudagrass response to shade is unknown.
Results from this research benefits superintendents in many aspects. First, this study
provides insight into the performance of Champion bermudagrass when grown under
108
shade in the field. Secondly, this research informs superintendents how to effectively
manage N when growing an ultradwarf bermudagrass cultivar when shading is prevalent.
Thirdly, the interactive effects of TE, various N rates, and Iron (Fe) were examined in a
reduced light environment. Finally, the effect of various N rates, TE, Fe, and various
light intensities were investigated to determine its effect on Champion bermudagrass
thatch accumulation over this two-year study period.
Materials and Methods
This research project was conducted at the Turfgrass Research Center, Clemson
University, Clemson, SC on Champion bermudagrass (Brown et al., 1997) field research
plots established by sprigs in July, 2003 with soil profile constructed to approximate
United States Golf Association (USGA) recommendations (USGA, 1993) (Illustration
D.13). Shade treatments consisted of control (no shade) and 55% full-day shade using a
neutral density, polyfiber black shade cloth (Glenn Harp and Sons, Inc., Tucker, GA)
supported by polyvinyl chloride (PVC) 183 cm in length and 152 cm in width with 2.54
cm diameter PVC pipes. Shade structures were 15 cm above the bermudagrass surface to
reduce early morning and late afternoon sunlight encroachment, yet maintain adequate
wind movement. Shade treatment duration was 15 June to 15 September 2006 and 2007.
All tents were removed nightly.
Nitrogen was applied every two weeks as urea (45-0-0) using a CO2–pressurized
backpack sprayer at rates of 147, 294, and 441 kg ha-1
yr-1
. Iron was tank mixed with N
at a rate of 2.7 kg a.i. ha-1
2wk-1
. Additional phosphorus (P) and potassium (K)
109
requirements were provided by potassium phosphate (K2HPO4) applied at 98 kg K ha-1
in
July, August, and September. Trinexapac-ethyl was applied at 0.02 kg ha-1
using the
emulsifiable concentrate (11.3% a.i.) every two weeks from 15 June to 31 August 2006
and 2007 using a CO2–pressurized backpack sprayer.
Plots were mowed daily at 3.2 mm throughout the study period. Hollow tine
aerification (1.3 cm diam. tines 10 cm in length with 5.0 cm spacing) occurred late June
and early August for both years. Disease was minimal, therefore no fungicides were
applied.
Data collection
Data collected included microenvironment conditions, visual TQ, clipping yield,
shoot chlorophyll concentration, thatch accumulation, thatch depth, and root total
nonstructural carbohydrates (TNC).
Microenvironment parameters included surface and soil temperature, wind
movement, and light quality and quantity. Surface and soil temperature, light quality,
and PPFD ( mol m-2
s-1
) were recorded on a clear, cloudless day at solar noon using an
indoor/outdoor thermometer (model #1455 and model #9840, Taylor, Oakbrook, IL),
spectroradiameter (Model LI-1800; LiCor, Inc., Lincoln, NE), and quantum radiometer
(Model LI-250, LiCor, Lincoln, NE), respectively. Wind movement was recorded twice
on days with a consistent breeze using an anemometer (model #CS-800, Clark Solutions,
Hudson, MA).
Visual TQ ratings were recorded day 1, week 4, 8, and 12 based on color, density,
texture, and uniformity of the bermudagrass surface. Quality was visually evaluated from
110
1 to 9, 1 = brown, dead turfgrass, 6 = minimal acceptable turfgrass, 9 = ideal green,
healthy turfgrass.
Clipping yield (g m-2
) was collected at week 6 and 12 for both years. Shoot tissue
was collected using a Toro® walk behind greens mower (Greenmaster® 800, The Toro
Company, Bloomington, MN) following one day of growth. Following clipping
collection, clippings were oven dried at 80oC for 48 hr and weighed to quantify shoot
production.
Shoot chlorophyll (mg g-1
) concentration was collected on same dates as clipping
yield. Fresh clippings were collected (as described above) from each plot and
immediately placed in a plastic bag inside a covered bucket to prevent sunlight
degradation. Clippings were weighed (0.1g) and placed in a glass test tube (1.0 cm in
width and 14.8 cm in length) with 10 mL of dimethyl sulfoxide (DMSO) to eliminate
shoot tissue grinding (Hiscox and Israelstam, 1979). Samples were incubated in 65 oC
water on a hot plate (PC-600, Corning, Corning, NY) for 1.5 hr and continuously shaken.
Upon completion, samples were passed through filter paper (Whatman 41, Whatman,
England) and remaining extract (2 mL) transferred into cuvettes. Absorbance values
were recorded at 663 nm and 645 nm wavelengths using a Spectrophotometer
(GenesysTM
20, ThermoSpectronic, Rochester, NY). Blanks were initially run and also
after every sixth sample. The following formula was used to calculate total shoot
chlorophyll: (mg g-1
) = (8.02 * D663 + 20.2 * D645) * 0.1 (Arnon, 1949).
Thatch accumulation (g) and depth (cm) were measured at week 12 for both
years. A bulk density sampler extracted one 154.4 cm3 core from each plot. Roots were
111
clipped at the base of the thatch layer and the remaining thatch sample was placed in an
80oC oven for 96 hrs and weighed. Thatch samples were then placed in a muffle furnace
(Benchtop Muffle Furnace LMF-A550, Omega Engineering, Inc., Stamford, CT) at
525oC for three hrs to provide ash organic weight (Snyder and Cisar, 2000). Samples
were weighed again and then subtracted from the original dry weight, which determined
thatch accumulation (g). Thatch depth (cm) was measured from five points on the soil
core and averaged using a ruler. Measurements were taken from bottom of the foliage to
the base of the thatch layer. Measurements were collected following oven drying.
Root TNC (mg g-1
) was collected at week 12 for both years. Root tissue was
harvested using a bulk density sampler which extracted 154.4 cm3 cores prior to sunrise
to minimize any diurnal fluctuations. Following soil removal, root tissue samples were
stored at -75oC until freeze dried at -40
oC for two wks to cease all metabolic activity.
Samples were then ground using an A-10 plant grinder (IKA Works, Inc., Wilmington,
NC). Grounded samples were rehydrated with 100 L of 80% ethanol (EtOH) and 2 mL
of 0.1 M sodium acetate buffer (pH 4.5) in glass test tubes 13 X 100 mm. Rehydrated
samples were placed in boiling water for 1 hr, cooled for 1 hr and repeated. Then, 2 mL
of invertase (Sigma I-4753, 433 units mg-1
) and amyloglucosidase (Sigma A-7255,
23,000 units g-1
) were added to solution. Samples were placed in water bath (40 – 45oC)
for three days and vortexed three times daily. TNC analysis was analyzed using Nelson‟s
Assay (1944), which determines glucose and fructose in plant tissue (Nelson, 1944;
Somogyi, 1945). A 25 L of aliquot was removed and two reagents (copper and arseno-
112
molybdate) were added to solution. Absorbance values were measured at 520 nm using a
spectrophotometer.
Data Analysis
Treatments were arranged in a randomized complete block design (RCBD) with
level of shade as a split-plot with three replications. Treatment effects were evaluated
using analysis of variance within the Statistical Analysis System (version 9.1, SAS
Institute, Cary, NC). Linear and quadratic responses were also examined when
appropriate to determine the impacts of light environment, N rates, and TE on parameters
measured. By week 4 of the study, all parameters (TQ, clipping yield, chlorophyll,
thatch, and TNC), did not have significant interactions between year I and II, therefore,
yearly data were pooled and statistically analyzed. Means separation was analyzed using
Fisher‟s least significant difference (LSD) test at P ≥ 0.05.
Results and Discussion
Microenvironment
Surface temperature under shade was reduced 7.8oC (45.4
oC in full-sunlight; 37.6
oC in 55% shade), while soil temperature under shade was reduced 2.2
oC (32.9
oC in full-
sunlight; 30.7 oC in 55% shade) compared to full-sunlight. Light intensity was reduced
by 55% (1891.4 mol m-2
s-1
full-sunlight; 833.9 mol m-2
s-1
55% shade) under the
shading material, however, no differences in light quality or wind movement were
detected due to shade structures position above the bermudagrass surface. Although light
113
quality impacts turfgrass growth (Wherley et. al., 2005), the focus of this study was light
quantity reduction.
Turfgrass Quality
Iron applications had minimal impacts on TQ, however, at week 4, main effect
means indicated Fe (5.9) improved TQ compared to untreated (5.6) plots (Table 7.1).
Munshaw et al. (2006) also noted Fe applications on field grown bermudagrass cultivars
were largely ineffective in consistently enhancing color and quality. However, Xu and
Mancino (2001) reported that applying Fe consistently increased two cool-season
turfgrasses leaf color. The ineffectiveness of Fe to provide increased TQ scores may be
related to daily clipping removal. Symptoms of Fe deficiency are often linked to sites
where daily mowing occurs (Turgeon, 2005). Also, Fe is quickly converted to insoluble
forms in the soil, which typically results in short-term visual responses following Fe
applications (Turgeon, 2005). At week 4, a linear response indicated that increasing N
under 55% full-day shade negatively impacted TQ scores. However, in the absence of
shade, increasing N rates linearly increased visual TQ scores. Applying N at 147 kg ha-1
yr-1
had an unacceptable TQ score of 5.4 in full-sunlight. Long (2006) also indicated
applying N at or below 488 kg ha-1
yr-1
resulted in poor TQ. After two TE applications,
minimal impacts on TQ scores were noted when grown under shade. A linear response
indicated TE significantly increased TQ of sun-grown Champion bermudagrass.
By week 8, applying N at a rate of 147 kg ha-1
yr-1
had greatest TQ compared to
293 and 437 kg ha-1
yr-1
N rates when grown in shade (Table 7.1) (Illustration D.14).
Although TQ scores were improved with lower N rates, TQ was below acceptable
114
Table 7.1. Turfgrass quality of a ‘Champion’ bermudagrass putting green
collected at day 1, weeks 4, 8, and 12 in response to three nitrogen rates (147, 294,
and 441 kg ha-1
yr-1
), plant growth regulator regimes (trinexapac-ethyl at 0 and
0.02 kg ha-1
2 wk-1
), iron applications (0 and 2.7 kg Fe ha-1
2wk-1
), and two light
environments (full-sunlight and 55% full-day shade) at Clemson University,
Clemson, SC in 2006 and 2007.
Light
Environment
Nitrogen
(N) Trinexapac-ethyl
(TE) Wk 4 Wk 8 Wk 12 kg ha-1
yr-1
Shade (S) 147
5.3 5.4 5.6
294
5.2 4.4 4.8
441
4.8 3.2 3.8
Full-sun (FS) 147
5.4 6.4 6.5
294
6.7 7.4 7.4
441
7.2 7.6 7.6
S
TE 5.1 5.1 5.7
No TE 5.0 3.5 3.8
FS
TE 6.8 7.0 7.4
No TE 6.0 7.3 7.0
S
0.0001 0.0001 0.0001
N
0.0003 0.0055 0.0005
TE
0.0101 0.0001 0.0001
S X N
0.0001 0.0001 0.0001
Linear S 0.0043 0.0001 0.0001
FS 0.0001 0.0001 0.0001
Quadratic S NS NS NS
FS 0.0306 NS 0.1106
S X TE
0.0018 0.0001 0.0001
Linear S NS 0.0001 0.0001
FS 0.0001 NS 0.0371
N X TE
NS NS NS
Linear
-- -- --
S X N X TE
NS NS NS †Turfgrass quality based on a scale of 1-9, 1=brown/dead turfgrass, 6=minimally acceptable
turfgrass, 9=healthy/green turfgrass. ‡NS, not significant at 0.05 probability level.
§Significant at 0.05 probability level.
115
threshold for all three N rates. Shade-grown bermudagrass TQ decline below acceptable
standards has also been noted in other field studies (Jiang et al., 2004; Bunnell et al.,
2005 a and b). Similar to week 4, increasing N rates under full-sunlight resulted in a
linear TQ increase. However, results may differ on a golf course due to a high traffic
environment. While the 147 kg ha-1
yr-1
N rate provided acceptable TQ (6.4) in full-
sunlight, this N rate may be too low to provide recuperative ability when exposed to daily
traffic and operations typical of a golf course environment. Long (2006) noted that 488
kg ha-1
yr-1
of N was not sufficient to maintain acceptable TQ. Differences may have
occurred between the studies because Long (2006) used a different N source (ammonium
sulfate) compared to urea used in this study. Also, the green used by Long (2006) was
still in a grow-in phase and may have required a higher annual N input than the
established bermudagrass green used in the present study. Unlike week 4, two months
following shade initiation, TE-treated plots (5.1) showed a linear TQ increase compared
to non TE-treated plots (3.5). However, it should be noted that TQ scores for TE-treated
plots were below the acceptable threshold of 6.
After 3 months of 55% full-day shade, fertilizing with lower N rates provided a
linear TQ increase compared to increasing N rates (Table 7.1). Also, in full-sunlight, a
yearly N rate of 147 kg ha-1
had lower TQ scores than 293 and 437 kg ha-1
yr-1
N rates,
however, all TQ scores remained above acceptable threshold. Trinexapac-ethyl
applications resulted in a linear TQ increase for full-sunlight and 55% full-day shade
plots (Illustration D.15). Bunnell et al. (2005b) noted TE-treated TifEagle bermudagrass
116
mowed at 3.2 mm had greater TQ scores compared to non TE-treated TifEagle when
grown under 4 hours of sunlight.
Clipping Yield
By week 6, under full-sunlight, increasing N rates linearly increased shoot growth
(Table 7.2). Also, when grown under shade at the low N rate, clipping yield was reduced
~93% compared to 293 and 437 kg ha-1
yr-1
N rate. This clipping yield reduction in
response to lower N rates likely led to TQ increases. Beard (1997) suggested a reduction
in lateral stem growth is likely the major factor for warm-season turfgrass decline in
shade. Therefore, in this study, a reduction in shoot growth due to low N rates reduced
the potential for excessive tissue removal, thereby, allowing the plant to conserve and
possibly re-allocate carbohydrate constituents within the plant. Also, TE provided
growth suppression under both full-sunlight and full-day shade environments. Under
55% shade and full-sunlight, TE linearly reduced shoot growth 110% and 63%,
respectively. In full-sunlight, McCullough et al. (2006a and 2007) also noted clipping
yield reductions in field grown TifEagle bermudagrass following TE applications, while
Ervin et al. (2007) noted a reduction in „Tifway‟ bermudagrass plant height when treated
with TE. In shade, Ervin et al. (2002) and Bunnell et al. (2005b) stated TE was effective
in suppressing clipping yield, while Qian et al. (1998) noted a reduction in plant height
following TE applications.
A linear and quadratic clipping yield response was noted as N rates increased
under shade by week 12 (Table 7.2). Also, a linear increase in clipping yield was noted
when grown under full-sunlight when N rates increased from 147 to 437 kg ha-1
yr-1
. At
117
Table 7.2. Clipping yield (g m-2
) of a ‘Champion’ bermudagrass putting green
collected at weeks 6 and 12 in response to three nitrogen rates (147, 294, and
441 kg ha-1
yr-1
), plant growth regulator regimes (trinexapac-ethyl at 0 and 0.02
kg ha-1
2 wk-1
), and two light environments (full-sunlight and 55% full-day
shade) at Clemson University, Clemson, SC in 2006 and 2007.
Clipping yield (g m-2
)
Light
Environment
Nitrogen
(N)
kg ha-1
yr-1
Trinexapac-ethyl
(TE) Week 6 Week 12
Shade (S) -- 12.4
Full-sun (FS) -- 3.5
TE -- 6.4
No TE -- 9.5
S 147 -- 6.4 6.9
294 -- 12.2 15.6
441 -- 12.4 14.6
FS 147 -- 1.2 1.6
294 -- 3.6 3.5
441 -- 5.8 5.4
S -- TE 6.7 --
-- No TE 14.1 --
FS -- TE 2.7 --
-- No TE 4.4 --
--
---------------P-----------
S 0.0001† 0.0001
N 0.0001 0.0001
TE 0.0001 0.0003
S X N 0.0199 0.0051
Linear S 0.0001 0.0001
FS 0.0001 0.0247
Quadratic S 0.0007 0.0013
FS NS‡ NS
S X TE 0.0001 NS
Linear S 0.0001 --
FS 0.0199 --
N X TE NS NS
118
Table 7.2. Clipping yield (g m-2
) of a ‘Champion’ bermudagrass putting green
collected at weeks 6 and 12 in response to three nitrogen rates (147, 293, and
437 kg ha-1
yr-1
), plant growth regulator regimes (trinexapac-ethyl at 0 and 0.02
kg ha-1
2 wk-1
), and two light environments (full-sunlight and 55% full-day
shade) at Clemson University, Clemson, SC in 2006 and 2007 (continued).
S X N X TE NS NS †Significant at 0.05 probability level.
‡NS, not significant at 0.05 probability level.
the study‟s end, shaded plots had a 2.5 unit clipping yield increase compared to full-
shoot growth became less pronounced during the study‟s duration. In this study, the last
application of TE was end of August and bermudagrass growth began to naturally
subside during the cooler temperatures and shorter days characteristic of September,
which probably resulted in continued shoot growth reductions. It appears TE‟s effect on
clipping yield suppression efficiency is dependent on turfgrass species, and TE rates and
application frequency (McCullough et al., 2007).
Chlorophyll
Iron did not impact chlorophyll concentration of Champion bermudagrass (Table
7.3). Similar results were noted by Stier and Rogers (2001) when Kentucky bluegrass
(Poa Pratensis L.) and supine bluegrass (Poa supina Schrad.) were subjected to shade
stress. Previous investigations have noted increased Fe availability in nutrient solution
medium enhances chloroplast development of Kentucky bluegrass, which led to an
increase in chlorophyll b production (Lee et al., 1996). In this study, it was possible that
Fe uptake was inhibited, Fe rates and frequency of application were insufficient, or a
reduced light environment restricts optimal Fe uptake. Iron uptake might have occurred,
119
Table 7.3. Total shoot chlorophyll concentration (mg g-1
) of a ‘Champion’
bermudagrass putting green collected at weeks 6 and 12 in response to three
nitrogen rates (147, 294, and 441 kg ha-1
yr-1
), plant growth regulator regimes
(trinexapac-ethyl at 0 and 0.02 kg ha-1
2 wk-1
), and two light environments
(full-sunlight and 55% full-day shade) at Clemson University, Clemson, SC in
2006 and 2007.
Chlorophyll (mg g-1
)
Light
Environment
Nitrogen (N)
kg ha-1
yr-1
Trinexapac-
ethyl (TE) Week 6 Week 12
Shade (S) 147 -- 2.88 2.34
294 -- 2.79 1.97
441 -- 2.73 1.94
Full-sun (FS) 147 -- 3.05 2.88
294 -- 3.40 3.02
441 -- 3.56 3.23
S -- TE 3.00 2.21
-- No TE 2.60 1.95
FS -- TE 3.37 2.99
-- No TE 3.32 3.09
-----------------P-------------
S 0.0001† 0.0001
N 0.0161 NS
TE 0.0001 NS
S X N 0.0001 0.0001
Linear S NS‡ 0.0003
FS 0.0001 0.0015
Quadratic S NS 0.0502
FS NS NS
S X TE 0.0023 0.0081
Linear S 0.0001 0.0033
FS NS NS
N X TE NS NS
S X N X TE NS NS †Significant at 0.05 probability level.
‡NS, not significant at 0.05 probability level.
120
however, Fe present in shoot tissue may have been removed due to daily mowing. Under
shade, the 147 kg ha-1
yr-1
N rate had 5% greater chlorophyll concentration compared to
the 437 kg ha-1
yr-1
N rate, however, a linear or quadratic response did not occur. A
linear increase in chlorophyll was noted as N rates increased under full-sunlight.
Applying N at 437 kg ha-1
yr-1
provided a 17% and 5% chlorophyll increase compared to
applying N at 147 and 293 kg ha-1
yr-1
, respectively. Applying TE linearly increased
chlorophyll concentration 15% compared to non TE-treated Champion bermudagrass
when grown under 55% full-day shade. Also, TE minimally increased Champion
bermudagrass chlorophyll concentration when grown under full-sunlight compared to
non TE-treated plots.
Unlike week 6, applying N at 147 kg ha-1
yr-1
showed a 21% linear increase in
chlorophyll concentration compared to the 437 kg ha-1
yr-1
N rate at week 12 when grown
under shade (Table 7.3). Also, sun-grown Champion had a linear increase (12%) in
chlorophyll as N rates increased. A linear chlorophyll increase (13%) was noted for TE-
treated plots compared to non TE-treated plots when grown in shade. This increase can
be attributed to a cell length reduction and cell density increase due to TE‟s influence
(Ervin and Koski, 2001). Under full-sunlight, Champion bermudagrass chlorophyll
concentration slightly decreased when TE was applied. However, in week 6, TE-treated
plots had a slight increase in chlorophyll concentration compared to non TE-treated plots.
This data seems to indicate TE applications (0.02 kg ha-1
2 wk-1
) had minimal impacts on
Champion bermudagrass chlorophyll concentrations when grown in full-sunlight.
Bunnell et al. (2005) also noted applying TE from June to August did not significantly
121
increase chlorophyll concentration of sun-grown TifEagle bermudagrass at a 3.2 mm
mowing height. Although, McCullough et al. (2006a) noted an 18% chlorophyll increase
early in the growing season for TE-treated TifEagle bermudagrass compared to non TE-
treated TifEagle, however, TE did not increase chlorophyll concentration at the end of the
growing season. Heckman et al. (2001c) noted a single TE application at multiple rates
enhanced chlorophyll concentration of Kentucky bluegrass (Poa Pratensis L.) cultivars.
It appears that TE initially enhances chlorophyll production early in the growing season,
however, repeated applications throughout the growing season at the same rates may be
less effective at promoting chlorophyll production. This could be attributed to the
dissipation of TE activity when temperatures are high. Beasley et al. (2007) noted in a
cool-season turfgrass that TE uptake was greatest during cooler temperatures, however,
TE dissipation was most rapid in periods of warm temperatures. Qian et al. (1998) noted
TE‟s lasting effect on zoysiagrass shoot height was greatest when temperatures were
cool, while more frequent TE applications were required during periods of high
temperatures. Therefore, in this study, the inability of TE to enhance chlorophyll
production during the growing season could be temperature related. Also, TE applied to
shaded plots consistently maintained higher shoot chlorophyll concentration compared to
non TE-treated plots due to temperature reductions typical of a shaded microenvironment
(Beard, 1973), thereby, possibly influencing TE‟s efficacy. The longevity of TE
enhancing physiological responses of turfgrasses in response to an abiotic stress and/or an
ideal environment may be related to several factors, including soil/surface temperature,
photoperiod, N rate, source, and timing, and TE application rate and frequency.
122
Thatch
Thatch accumulation was minimally impacted by treatments (Table 7.4).
However, Champion grown under shade had a 40% decrease in thatch accumulation
compared to full-sunlight plots. Similar to thatch accumulation, full-sunlight grown
Champion produced 29% greater thatch depth compared to shade grown Champion.
Excessive thatch accumulation typically occurs when organic matter production, such as
clippings or stolons, is greater than organic matter decomposition (Beard, 1973), which is
often linked to accelerated shoot growth. Due to reductions in shoot biomass (Table 7.2)
of shade-grown Champion bermudagrass, this biomass decline most likely led to reduced
thatch accumulation and thickness. Trinexapac-ethyl applications and higher N rates
both resulted in slightly greater thatch depth compared to non TE-treated and lower N
plots. However, Fagerness et al. (2001) indicated repeated TE applications (0.11 kg a.i.
ha-1
) did not affect thatch development, rather increased shoot density, while percent
green canopy tissue accelerated thatch accumulation. In full-sunlight, thatch depth
showed a linear and quadratic response as N rates increased. Nitrogen applied at 293 kg
ha-1
yr-1
showed a 26% and 5% increase in thatch thickness compared to N rates of 147
and 437 kg ha-1
yr-1
, respectively.
Carbohydrates
Root total non-structural carbohydrates were minimally impacted in this study by
N rates or TE applications (Table 7.4). Main effect means noted a 4% increase in root
TNC for Champion bermudagrass grown under full-sunlight compared to shade. Bunnell
123
Table 7.4. Thatch accumulation, thatch thickness, and root total non-structural
carbohydrates of a ‘Champion’ bermudagrass putting green collected at week
12 in response to three nitrogen rates (147, 294, and 441 kg ha-1
2 wk-1
), plant
growth regulator regimes (trinexapac-ethyl at 0 and 0.02 kg ha-1
2 wk-1
), and
two light environments (full-sunlight and 55% shade) at Clemson University,
Clemson, SC in 2006 and 2007.
Light
Environment Nitrogen
(N) Trinexapac-
ethyl (TE)
Thatch
Accumulation
(g)
Thatch
Thickness
(cm)
Root
TNC (mg g
-1)
Shade (S) 5.7 2.8 33.8
Full-sun (FS) 8.0 3.6 35.2 147 -- 2.9 -- 294 -- 3.3 -- 441 -- 3.3 --
TE -- 3.3 --
No TE -- 3.1 --
S 147 -- 2.7 -- 294 -- 2.7 -- 441 -- 2.9 --
FS 147 -- 3.1 --
294 -- 3.9 --
441 -- 3.7 --
----------------------------P----------------------
S 0.0001† 0.0001 0.0238
N NS‡ 0.0082 NS
TE NS 0.0447 NS
S X N NS 0.0221 NS
Linear S -- NS -- FS -- 0.0044 -- Quadratic S -- NS -- FS -- 0.0060 --
S X TE NS NS NS
S X N X TE NS NS NS †Significant at 0.05 probability level.
‡NS, not significant at 0.05 probability level.
124
et al. (2005b) reported TifEagle bermudagrass root TNC collected in mid-August grown
under shade varied in response to sunlight hours and management practices.
Conclusion
Champion bermudagrass is unable to provide an acceptable putting green standard
when grown under moderate (55%) full-day shade. However, altering PGR and N
applications enhanced the performance of Champion bermudagrass when grown under
shade. Applying N at 147 kg ha-1
yr-1
significantly improved TQ of Champion when
grown under shade compared to higher N rates. Applying low N rates reduced vertical
shoot growth, thereby, minimizing the amount of shoot tissue removed from daily
mowing. Also, the N rate of 437 kg ha-1
yr-1
reduced shoot chlorophyll 20% compared to
N rate of 147 kg ha-1
yr-1
when grown under shade. Similar to reducing N, applying TE
every two weeks improved TQ and chlorophyll concentrations of shade-grown Champion
bermudagrass.
Based on this study, recommendations for superintendents can be made to manage
bermudagrass greens when light to moderate shade exists. Reducing N rates and
routinely applying TE can improve the performance of Champion bermudagrass in a
shaded environment. However, applying Fe at 2.7 kg a.i. ha-1
2wk-1
had minimal impacts
based on parameters measured. While Champion bermudagrass performance can be
enhanced through management practices, visual TQ will inevitably decline if shade
intensity is too great or shade duration is too long. It has been suggested that
bermudagrass greens require ~36 mol m-2
d-1
of sunlight (Bunnell et al., 2005a; Miller et
125
al., 2005). Also, time of shading is also a relevant consideration when planting a
bermudagrass green (Bunnell et al., 2005a).
126
CHAPTER VIII
ALTERED LIGHT SPECTRAL QUALITIES IMPACTS ON WARM-SEASON
TURFGRASS GROWTH AND DEVELOPMENT
Introduction
Turfgrass growth and development under shade is inhibited by reduced
photosynthesis (Jiang et al., 2004; Miller et al., 2005), increased disease pressure (Beard,
1965; Vargas and Beard, 1981) due to extended morning dew duration (Dudeck and
Peacock, 1992; Williams et al., 1996), reduced carbohydrate production (Bunnell et al.,
2005a; Bunnell et al., 2005c), tree root competition (Whitcomb, 1972; Whitcomb and
Roberts, 1973), and reduced lateral stem growth (Beard, 1997). Another factor limiting
turfgrass growth and development under tree shade is various qualities of light filtered by
trees. The photosynthetic active radiation (PAR) available for plant growth is between
400 and 700 nm with ~90% absorbed by the plant and the remainder reflected at the leaf
surface or transmitted through the leaf (Taiz and Zeiger, 2006). Blue light occurs from
wavelengths 400 to 500 nm, green light 500 to 600 nm, red light 600 to 700 nm, and far-
red light 700 to 800 nm (Taiz and Zeiger, 2006). In nature, trees alter spectral quality
available for turfgrass development (Bell et al., 2000), however, limited research has
investigated the light specific tree species filter in highly maintained turfgrass
environments. Also, most shade research has focused on light quantity by filtering shade
with black neutral cloths (Bell and Danneberger, 1999; Koh et al., 2003; Steinke and
Stier, 2003; Bunnell et al., 2005b; Baldwin et al., 2008).
127
Gaskin (1965) demonstrated a green shade cloth (75% light reduction) had
different light quality spectrums compared to white oak (Quercus alba L.) and maple
(Acer sp.) tree shade. McBee (1969) noted post oak (Quercus stellata Wang.) canopy
filtered wavelengths between 600 to 675 nm. Using a color temperature meter, which
contains two photocells deriving light quality indicating relative amount of blue and red
light, McKee (1963) indicated dense herbaceous shade such as lambsquarter
(Chenopodium album L.), ragweed (Ambrosia trifida L.), and smartweed (Polygonum
pensylvanicum L.) depleted blue wavelengths, while trees with a high canopy filtered red
wavelengths. Bell et al. (2000) noted conifer and deciduous tree shade (R:FR<1.0)
altered spectral quality available for turfgrass growth.
While previous research have demonstrated variations of light available for
turfgrass growth depending on the source of shade, few reports have investigated light
quality impacts for turfgrass growth and development. McBee (1969) noted blue light
minimized stem elongation, while red light enhanced stem elongation for selected
bermudagrass (Cynodon spp.) cultivars. Also, shorter wavelengths (blue light) were most
important for a successful turfgrass stand, while minimal red light was necessary for
normal turfgrass appearance. McVey et al. (1969) also noted blue light significantly
enhanced quality and color while reducing clipping fresh weight production and vertical
shoot elongation in „Windsor‟ Kentucky bluegrass (Poa pratensis L.) and „Tifgreen‟
bermudagrass. In a recent study, Wherely et al. (2005) subjected „Plantation‟ (shade-
tolerant) and „Equinox‟ (shade-sensitive) tall fescue (Festuca arundinacea Schreb.) to
deciduous (Acer spp. and Fraxinus spp., R:FR - 0.428) and neutral (R:FR – 1.021) shade.
128
Both cultivars grown in deciduous shade produced significantly less tillering (~57%),
greater leaf width (~53%), higher chlorophyll levels (~40%), and greater leaf thickness
(~24%) than neutral shade (92% light reduction) grown cultivars. High or low R:FR
ratios did not impact root growth.
It has been noted that changes in spectral light quality influences plant
morphogenesis, while a photosynthetic photon flux density (PPFD) reduction (neutral
shade) affects growth and production parameters (Stuefer and Huber, 1998). However,
physiological and morphological studies of warm-season turfgrasses in response to
various light spectrums are lacking. This type of research could benefit turfgrass
managers in many aspects. First, this study would determine how various spectral
qualities of light affect warm-season turfgrasses performance. This information would
allow turfgrass managers to make informed decisions when trees or tree limbs are
considered for removal. Secondly, this research project would further the understanding
of why warm-season turfgrasses respond differently when grown under shade. Lastly, a
limited number of studies have demonstrated tree species alter light spectral quality in a
turfgrass setting (McKee, 1963; McBee, 1969; Bell et al., 2000). Taking results from
these previous studies and continued research would specify the type of light certain tree
species filter. Therefore, this research is the first step in providing a blueprint for golf
course design by matching turfgrass cultivars that perform well under specific light
filtered by individual tree species. Therefore, the author hypothesized that different light
spectrums, not just light quantity, would alter morphological and physiological status of
129
selected warm-season species to varying degrees and selected turfgrasses would show
genetic differences in response to various light treatments.
Materials and Methods
This research included two repeated studies at the Clemson University
Greenhouse Research Complex. Study I was conducted from 15 April 2007 – 15 June
2007. Greenhouse conditions averaged 26oC / 22
oC day/night temperature and 60%
relative humidity. Study II was conducted from 6 July 2007 – 31 August 2007.
Greenhouse conditions averaged day/night temperature of 28 oC / 23
oC and 70% relative
humidity.
Each study consisted of five light treatments including a control (full-sunlight)
with three replications in a randomized complete block design. Light treatments include
four different color shade cloths filtering wavelengths 560 - 720 nm (blue shade cloth),
360 – 520 nm (yellow shade cloth), 360 - 560 nm (red shade cloth) and 360-720 (black
shade cloth) (Figure 8.1) (Illustration D.16). Red to far red ratio for each cloth is ~1.171,
while percent light reduction for each cloth was ~65%. Light quality and quantity were
measured on a clear, cloudless day at solar noon using a spectroradiameter (Model LI-
1800; LiCor, Inc., Lincoln, NE), and a quantum radiometer (Model LI-250, LiCor,
Lincoln, NE), respectively.
Turfgrasses selected were „Tifway‟ and „Celebration‟ bermudagrass (Cynodon
dactylon X C. transvaalensis), „Sea Isle 2000‟ seashore paspalum (Paspalum vaginatum
Swartz.), and „Diamond‟ zoysiagrass (Zoysia matrella (L.) Merr). Tifway and
130
Figure 8.1. Portion of light spectrum filtered by the shading material selected for a
greenhouse experiment.
Celebration plugs of sod were collected from the 2002 NTEP bermudagrass trials at the
Clemson University Research Center and washed free of soil with roots clipped. Sea Isle
2000 was provided by Modern Turf (Rembrant, SC 29128). Diamond zoysiagrass was
provided by Atlanta Athletic Club (Johns Creek, GA 30097). All turfgrasses were placed
in lysimeters 15 cm in diameter and 46 cm in height filled with 10.14 cm of gravel (8mm
to 10 mm in diameter) and 30.48 cm of 85% sand and 15% peat as growth media (v:v)
and allowed four weeks to establish before treatment initiation. Lysimeters were mowed
131
every other day at 1.3 cm using a handheld 7.2 volt cordless shear (model #ssc1000,
Black and Decker, Towson, MD) and watered daily (if necessary) to prevent wilt.
During the four-week establishment period prior to shade treatment initiation, fertility
was provided weekly using a combination of 10N-1.3P-4.2K and 5N-0P-5.8K liquid
fertilizers (Progressive Turf, LLC., Ball Ground, GA) at a rate 19.4 kg N ha-1
. Once light
treatments were initiated, turfgrasses were fertilized at a rate of 9.7 kg N ha-1
weekly. A
CO2-pressurized backpack sprayer was used to apply all fertilizers (107 gal ac-1
).
Lysimeters were moved every two weeks to minimize any location effects in the
greenhouse.
Parameters Measured
Data collection included canopy and soil temperature, visual TQ, clipping yield,
lateral spread, total shoot chlorophyll, shoot width, total root biomass, root length
density, specific root length, and root and shoot TNC.
Canopy and soil temperature were recorded on a clear, cloudless day at solar noon
using an indoor/outdoor thermometer (model #1455 and model #9840, Taylor, Oakbrook,
IL).
Visual TQ ratings were measured weekly based on color, density, texture, and
uniformity of the turfgrass surface. Quality was visually evaluated from 1 to 9, 1 =
brown, dead turfgrass, 6 = minimal acceptable turfgrass, 9 = ideal green, healthy
turfgrass.
Clipping yield (g m-2
) was collected at week 2, 4, and 6 following two full days of
growth. Lysimeters were tilted at a 45o angle and mowed with a 7.2 volt cordless shear
132
(model #ssc1000, Black and Decker, Towson, MD). Clippings fell onto poster board
(122 cm by 122 cm) and then placed into brown bags. Turfgrasses were not mowed for
three days prior to collecting clippings. Following clipping collection, clippings were
oven dried at 80oC for 48 hr and weighed to quantify shoot production.
Lateral spread (g) was collected at week 2, 4, and 6. Stolons were allowed to
extend the exterior of the lysimeter for two week periods. Every two weeks, shoot
growth exterior of the lysimeter was collected with a pair of scissors. The collected
biomass was then oven dried at 80oC for 48 hr and weighed.
Shoot width (mm) was measured at weeks 3 and 6. Five fully expanded leaves
from each lysimeter were randomly selected. For each leaf, leaf blade width across the
entire leaf blade was measured 1.5 mm from the base of each individual leaf using a
Buffalo 6” stainless steel digital caliper (Buffalo #SSDC6).
Shoot chlorophyll (mg g-1
) was collected at weeks 4 and 8. Fresh clippings were
collected from each lysimeter and immediately placed in a plastic bag inside a covered
bucket to prevent sunlight degradation. Clippings were weighed (0.1g) and placed in a
glass test tube (1.0 cm in width and 14.8 cm in length) with 10 mL of dimethyl sulfoxide
(DMSO), which eliminates shoot tissue grinding to extract chlorophyll (Hiscox and
Israelstam, 1979). Samples were incubated in 65 oC water on a hot plate (PC-600,
Corning, Corning, NY) for 1.5 hr and continuously shaken. Upon completion, samples
were passed through filter paper (Whatman 41, Whatman, England) and remaining
extract (2 mL) transferred into cuvettes. Absorbance values were recorded at 663 nm and
645 nm wavelengths using a spectrophotometer (GenesysTM
20, ThermoSpectronic,
133
Rochester, NY). Blanks were initially run and also after every sixth sample. The
following formula was used to calculate total shoot chlorophyll: (mg g-1
) = (8.02 * D663 +
20.2 * D645) * 0.1 (Arnon, 1949).
Total root biomass, root length density (mm cm-3
) (RLD), and specific root length
(cm mg-1
) (SRL) were determined at week 8. Roots were extracted from the entire
lysimeter at washed free of soil using a 1 mm sieve. Once all soil was completely
removed from each soil plug using tap water, roots were clipped from shoot tissue base.
Prior to placing the roots in an oven (80.0 oC) for 48 hr to quantify root biomass, a root
measuring software, WinRhizo Pro (Regent Instruments Inc., Quebec, Qc, Canada),
analyzed scanned root images for RLD and SRL. WinRhizo provides a computerized
method of measuring RLD (total root length (mm) per volume of soil (cm3) as described
by Tennant (1975). For SRL, a ratio of root length to root dry weight was calculated to
determine the amount of root length per milligram of dry weight (cm mg-1
).
Root TNC (mg g-1
) was collected at week 8, while shoot TNC (mg g-1
) was
collected weeks 4 and 8 for both years. Root tissue was harvested using a bulk density
sampler which extracted 154.4 cm3 (10.2 cm in depth) cores prior to sunrise to minimize
any diurnal fluctuations. Following soil removal, root tissue samples were stored at -
75oC until freeze dried at -40
oC for two wks to cease all metabolic activity. For shoot
TNC, shoot tissue was collected prior to sunrise, wrapped in aluminum foil and stored at
75oC until freeze dried at -40
oC for two wks to cease all metabolic activity. Samples
were then ground using an A-10 plant grinder (IKA Works, Inc., Wilmington, NC).
Grounded samples were rehydrated with 100 L of 80% ethanol (EtOH) and 2 mL of 0.1
134
M sodium acetate buffer (pH 4.5) in glass test tubes 13 X 100 mm. Rehydrated samples
were placed in boiling water for 1 hr, cooled for 1 hr and repeated. Two mL of invertase
(Sigma I-4753, 433 units mg-1
) and amyloglucosidase (Sigma A-7255, 23,000 units g-1
)
were then added to solution. Samples were placed in water bath (40 – 45oC) for three
days and vortexed three times daily. TNC analysis was analyzed using Nelson‟s Assay
(1944), which determines glucose and fructose in plant tissue (Nelson, 1944; Somogyi,
1945). For root TNC, 50 L of aliquot was removed, while 100 L of aliquot was
removed for shoot TNC (Waltz, 2005). Then, two reagents (copper and
arsenomolybdate) were added to solution and absorbance values were measured at 520
nm using a spectrophotometer.
Data Analysis
Treatments were arranged in a randomized complete block design with 3
replications. All statistical computations were conducted using analysis of variance
(ANOVA) within the Statistical Analysis System (version 9.1, SAS Institute, Cary, NC).
Means were separated by the Fisher‟s Least Significant Difference (LSD) test with an
alpha of 0.05. Under full-sunlight, significant differences occurred for clipping yield,
lateral spread, shoot width, shoot chlorophyll concentration, and root length density,
therefore, relative values were calculated to determine the impact different types of shade
had on each turfgrass. For root and shoot TNC and SRL, no significant treatment by
species interactions occurred, therefore, main effect means are presented. Data are
pooled for both repeated studies as no significant study by treatment interaction occurred.
135
Results
Microenvironment
Canopy temperature under each shade cloth was reduced 15oC (46
oC in full-
sunlight; 31 oC in shade), while soil temperature under shade cloth was reduced 2
oC (31
oC in full-sunlight; 29
oC in shade) compared to full-sunlight.
Full-sunlight
Turfgrasses performance significantly varied when grown under full-sunlight (Table
1). Tifway produced 50% greater clipping yield than Celebration at week 2, while
similar trends continued in week 4. By week 6, Diamond had greatest clipping yield
(~75%) compared to all other turfgrasses. At week 2, Celebration lateral spread was
60% greater than Tifway, while Diamond and Sea Isle 2000 were similar. By week 6,
Sea Isle 2000 and Celebration had ~1.0 unit lateral spread increase compared to
Diamond and Tifway, respectively. For shoot width, at week 8, Diamond had 160%,
94%, and 69% thinner leaf blade than Sea Isle 2000, Celebration, and Tifway,
respectively. Celebration and Tifway produced ~52% and ~29% greater chlorophyll
concentrations at week 3 compared to Diamond and Sea Isle 2000, respectively. At
week 6, Celebration showed 74% and 34% greater chlorophyll than Diamond and Sea
Isle 2000, respectively. Sea Isle 2000 produced 0.8 unit greater root biomass than
Celebration and ~3.2 unit greater root biomass than Diamond and Tifway (Illustration
D.17). Meanwhile, Celebration showed a ~1.3 unit increase in root biomass compared
to Diamond and Tifway. For RLD, under full-sunlight, Sea Isle 2000 (10.7 mm cm-3
)
136
Table 8.1. Clipping yield (g m-2
), lateral spread (g), shoot width (mm), shoot
chlorophyll (mg g-1
), root mass (g m-2
), and root length density (mm cm-3
) of
'Diamond' zoysiagrass, 'Sea Isle 2000' seashore paspalum, 'Celebration'
bermudagrass, and 'Tifway' bermudagrass under full-sunlight.
Clipping
Yield
(g m-2
)
Lateral
Spread
(g)
Shoot
Width
(mm)
Chlorophyll
(mg g-1
)
Root
Mass
(g m-2
)
Root
Length
Density
(mm cm-3
)
Treatment -----------------------------------------Week 2------------------------------------
Diamond† 0.19 0.48 -- -- -- --
Sea Isle
2000 0.15 0.54 -- -- -- --
Celebration 0.16 0.64 -- -- -- --
Tifway 0.24 0.40 -- -- -- --
LSD 0.05‡ 0.17 -- -- -- --
-----------------------------------------Week 3------------------------------------
Diamond -- -- -- 1.76 -- --
Sea Isle
2000 -- -- -- 1.87 -- --
Celebration -- -- -- 2.74 -- --
Tifway -- -- -- 2.34 -- --
LSD -- -- -- 0.42‡ -- --
-----------------------------------------Week 4------------------------------------
Diamond 0.26 0.40 0.39 -- -- --
Sea Isle
2000 0.18 0.53 0.94 -- -- --
Celebration 0.19 0.61 0.85 -- -- --
Tifway 0.25 0.31 0.65 -- -- --
LSD 0.03‡ 0.11 0.10 -- -- --
-----------------------------------------Week 6------------------------------------
Diamond 0.33 0.37 -- 1.71 -- --
Sea Isle
2000 0.16 0.58 -- 2.21 -- --
Celebration 0.16 0.59 -- 2.97 -- --
Tifway 0.23 0.29 -- 2.62 -- --
LSD 0.06‡ 0.11 -- 0.53 -- --
-----------------------------------------Week 8------------------------------------
Diamond -- -- 0.48 -- 0.19 2.6
Sea Isle
2000 -- -- 1.25 -- 0.86 10.7
137
Table 8.1. Clipping yield (g m-2
), lateral spread (g), shoot width (mm), shoot
chlorophyll (mg g-1
), root mass (g m-2
), and root length density (mm cm-3
) of
'Diamond' zoysiagrass, 'Sea Isle 2000' seashore paspalum, 'Celebration'
bermudagrass, and 'Tifway' bermudagrass under full-sunlight (continued).
Celebration -- -- 0.93 -- 0.47 6.5
Tifway -- -- 0.81 -- 0.22 3.8
LSD -- -- 0.11‡ -- 0.17 1.20
†Diamond: 'Diamond' zoysiagrass, 'Sea Isle 2000' seashore paspalum, 'Celebration'
bermudagrass, and 'Tifway' bermudagrass. ‡Values within a column followed by the same letter are not significantly different at
P≤0.05 by protected LSD.
LSD = Least significant difference.
had greatest RLD, followed by Celebration (6.5 mm cm-3
), Tifway (3.8 mm cm-3
), and
Diamond (2.6 mm cm-3
).
Shade
Turfgrass Quality
Minimal TQ differences were noted between turfgrasses maintained in full-
sunlight (Table 8.2). Following 1 wk of shade, Tifway was the only turfgrass to drop
below the acceptable threshold of 6. Celebration grown under black shade decreased TQ
by ~0.6 units compared to other shading material. Diamond and Sea Isle 2000 did not
show any significant TQ decreases compared to full-sunlight treatment. Comparing
turfgrasses, Diamond and Sea Isle 2000 had greater TQ scores than the bermudagrass
cultivars for most shade treatments. Also, Celebration produced greater TQ than Tifway
under yellow (1.0 unit) and blue (1.0 unit) shade.
By week 4, all turfgrasses TQ began to decline in response to shade (Table 8.2).
Only Diamond was able to remain above the acceptable threshold of 6 under black shade.
Within each turfgrass, black shade consistently showed greatest TQ declines compared to
138
other shade colors. Yellow, red, and blue shade had similar TQ scores. Celebration
maintained ~1.7 unit greater TQ than Tifway under all shade treatments. Meanwhile, Sea
Isle 2000 had ~0.8 unit TQ increase than Celebration when grown under blue and black
shade.
At the conclusion of the study, Diamond remained above acceptable TQ
threshold, however, a TQ decline was noted compared to full-sunlight (Table 8.2).
Unlike week 4, yellow and red shade TQ were similar for all turfgrasses, however, blue
shade showed ~0.8, ~0.6, ~1.3, and ~1.4 TQ unit decline for Diamond, Sea Isle 2000,
Celebration, and Tifway, respectively, compared to yellow and red shade (Illustration
D.18). Diamond had a 1.8, 3.2, and 4.5 unit greater TQ than Sea Isle 2000, Celebration,
and Tifway, respectively, under black shade. The most shade-sensitive turfgrass was
Tifway as TQ scores were below 4 under all shade treatments.
Clipping Yield
At week 2, black shade reduced Celebration and Tifway clipping yield ~0.63 and
~1.16 units, respectively, compared to yellow, red and blue shade (Table 8.3). Diamond
and Sea Isle 2000 grown under black and blue shade had ~75% and ~52% less clipping
yield compared to yellow shade. Comparing turfgrasses, under yellow and black shade,
Tifway clipping yield was reduced ~0.70 and ~1.26 units, respectively, compared to other
turfgrasses. Meanwhile, Celebration produced 30% and 64% greater clipping yield than
Diamond under red and blue shade, respectively.
139
Table 8.2. Turfgrass quality of 'Diamond' zoysiagrass, 'Sea Isle 2000' seashore
paspalum, 'Celebration' bermudagrass, and 'Tifway' bermudagrass affected by
full-sunlight and various types of filtered light (~65% reduction) in a
greenhouse study.
---------------------------------------Week 2-----------------------------------
Treatment Diamond Sea Isle 2000 Celebration Tifway LSD
Sun† 8.2 7.8 7.8 7.3 NS
Yellow 7.8 7.7 7.0 6.0 0.61§
Red 8.0 7.2 6.8 6.3 0.66
Blue 8.0 7.5 7.0 6.0 0.35
Black 7.8 7.2 6.3 5.8 0.61
LSD NS NS 0.54‡ 0.54
---------------------------------------Week 4-----------------------------------
Sun 8.3 8.2 7.8 7.5 0.56§
Yellow 7.3 6.8 6.2 4.7 0.66
Red 7.7 6.5 6.3 5.0 0.56
Blue 7.5 6.5 5.7 3.3 0.71
Black 6.8 5.5 4.7 3.3 0.66
LSD 0.58‡ 0.49 0.70 0.70
---------------------------------------Week 6-----------------------------------
Sun 8.2 7.8 7.5 7.7 NS
Yellow 7.2 5.7 5.0 3.7 0.61§
Red 7.3 5.8 5.5 4.0 0.66
Blue 6.5 5.2 4.0 2.5 0.75
Black 6.0 4.2 2.8 1.5 0.61
LSD 0.58‡ 0.62 0.62 0.67
†Sun: full-sunlight control, Yellow: filters <520 nm, Red: filters <560nm, Blue:
filters >560, and Black: filters all wavelengths. ‡Values within a column within each week followed by the same letter are not
significantly different at P≤0.05 by protected LSD. §Values within a row within each week followed by the same letter are not
significantly different at P≤0.05 by protected LSD.
Turfgrass quality based on a scale of 1-9, 1=brown/dead turfgrass, 7=minimally
acceptable turfgrass, 9=healthy/green turfgrass.
LSD = Least significant difference, NS = not significant.
140
Table 8.3. Relative clipping yield of 'Diamond' zoysiagrass, 'Sea Isle 2000' seashore
paspalum, 'Celebration' bermudagrass, and 'Tifway' bermudagrass affected by
full-sunlight and various types of filtered light (~65% reduction) in a greenhouse
study.
------------------------------------------Week 2-------------------------------------
Treatment Diamond Sea Isle 2000 Celebration Tifway LSD
Yellow† 119.8 126.8 143.9 76.5 39.54
§
Red 101.1 97.8 131.4 88.2 28.09
Blue 69.3 91.0 114.3 76.3 33.42
Black 67.9 63.2 79.7 31.1 20.58
LSD 19.83‡ 34.91 30.94 36.39
------------------------------------------Week 4-------------------------------------
Yellow 100.9 105.9 110.7 82.4 NS
Red 77.1 90.2 100.1 70.4 NS
Blue 61.2 65.8 71.9 70.7 NS
Black 42.7 33.7 41.2 29.3 NS
LSD 22.94‡ 24.92 31.22 27.80
------------------------------------------Week 6-------------------------------------
Yellow 69.8 102.7 99.9 67.1 27.17§
Red 63.7 86.4 94.9 54.7 20.04
Blue 60.7 74.5 75.7 38.2 28.62
Black 31.3 39.7 36.7 21.4 NS
LSD 17.08‡ 29.32 28.11 17.24
†Yellow: filters <520 nm, Red: filters <560nm, Blue: filters >560, and Black: filters all
wavelengths. ‡Values within a column within each week followed by the same letter are not
significantly different at P≤0.05 by protected LSD.
§Values within a row within each week followed by the same letter are not significantly
different at P≤0.05 by protected LSD.
LSD = Least significant difference, NS = not significant.
At week 4, no differences were detected between turfgrasses for any shade
treatment (Table 8.3). Black shade reduced Tifway clipping yield ~1.5 units compared to
yellow, red, and blue shade. Also, Diamond showed a 37% (red shade), 63% (blue
shade), and 136% (black shade) clipping yield reduction compared to yellow shade. For
141
Sea Isle 2000, compared to full-sunlight, yellow shade increased clipping yield 6%, while
black shade reduced clipping yield 66%. Similarly, yellow shade increased Celebration
clipping yield 11%, while blue and black shade reduced clipping yield ~44% compared to
full-sunlight.
By week 6, clipping yield differences between yellow and red shade and between
red and blue shade were not detected for any turfgrasses (Table 8.3). However, Tifway
grown under blue shade had a reduced clipping yield 76% compared to yellow shade.
Compared to other shade types, black shade reduced clipping yield ~0.89, ~1.21, and
~1.46 units for Diamond, Sea Isle 2000, and Celebration, respectively. Celebration and
Tifway clipping yield decreased ~10% and ~47% under yellow, red, and blue shade
compared to full-sunlight. Diamond clipping yield reduced ~41% compared to Sea Isle
2000 when grown under yellow and red shade. Meanwhile, Celebration produced 49%,
73%, and 98% greater clipping yield under yellow, red, and blue shade, respectively,
compared to Tifway.
Lateral Spread
At week 2, lateral spread of Diamond grown under shade was not impacted (Table
8.4). For other turfgrasses, lateral spread between yellow and red shade were similar,
while no differences were noted between red and blue shade. However, Celebration and
Tifway lateral spread reduced ~0.65 and ~1.79 units, respectively, under black shade
compared to yellow, red, and blue shade. Sea Isle 2000 grown under red shade had 40%
less lateral spread than yellow shade. Celebration showed 63% and 128% greater lateral
spread than Tifway when grown under red and black shade, respectively. Meanwhile,
142
Table 8.4. Relative lateral spread of 'Diamond' zoysiagrass, 'Sea Isle 2000'
seashore paspalum, 'Celebration' bermudagrass, and 'Tifway' bermudagrass
affected by full-sunlight and various types of filtered light (~65% reduction) in a
greenhouse study.
-----------------------------------------Week 2------------------------------------
Treatment Diamond Sea Isle 2000 Celebration Tifway LSD
Yellow† 101.7 93.4 69.2 57.7 28.87
‡
Red 76.8 90.9 76.9 47.1 27.91
Blue 66.4 66.9 72.5 48.0 NS
Black 73.9 52.8 44.3 19.4 24.76
LSD NS 25.37§ 15.76 20.73
-----------------------------------------Week 4------------------------------------
Yellow 97.1 80.7 65.9 42.4 22.91‡
Red 63.7 61.0 46.3 52.2 NS
Blue 53.9 38.4 39.0 27.7 12.61
Black 47.1 24.6 15.1 15.5 11.12
LSD 25.97§ 14.78 9.78 16.05
-----------------------------------------Week 6------------------------------------
Yellow 99.0 73.3 49.7 52.9 29.16‡
Red 73.0 54.4 40.9 36.3 24.24
Blue 56.9 39.8 32.9 19.1 12.36
Black 40.8 18.5 8.9 6.8 12.36
LSD 30.72§ 20.61 9.34 16.98
†Yellow: filters <520 nm, Red: filters <560nm, Blue: filters >560, and Black: filters all
wavelengths. ‡Values within a row within each week followed by the same letter are not
significantly different at P≤0.05 by protected LSD.
§Values within a column within each week followed by the same letter are not
significantly different at P≤0.05 by protected LSD.
LSD = Least significant difference, NS = not significant.
143
Celebration and Sea Isle 2000 lateral spread were similar. Diamond produced ~0.62 and
~1.74 unit greater lateral spread than Celebration and Tifway when grown under yellow
and black shade, respectively.
At week 4, yellow shade-grown Diamond produced greater lateral spread than red
(52%), blue (80%), and black (106%) shade (Table 8.4). Blue shade reduced lateral
spread compared to red shade for Sea Isle 2000 (59%) and Tifway (88%). Blue and
black shade impacted lateral spread similarly for Diamond, Sea Isle 2000, and Tifway,
however, black shade reduced Celebration lateral spread 1.6 units compared to blue
shade. Comparing bermudagrass cultivars, Celebration maintained greater lateral spread
when grown under yellow shade (55%) than Tifway. Under blue and black shade,
Diamond showed ~0.58 and ~1.69 unit greater lateral spread, respectively, than Sea Isle
2000, Celebration, and Tifway. Similar to week 2, lateral spread variation between Sea
Isle 2000 and Celebration did not occur.
At week 8, black shade increased lateral spread 1.2 and 2.7 units for Sea Isle 2000
and Celebration, respectively, compared to blue shade (Table 8.4). Sea Isle 2000 was the
only cultivar where red shade reduced lateral spread (35%) compared to yellow shade.
Compared to black shade, red shade reduced Diamond, Sea Isle 2000, Celebration, and
Tifway lateral spread by 0.81, 1.94, 3.60, and 4.34 units, respectively. When grown
under blue shade, Celebration maintained 72% greater lateral spread than Tifway
bermudagrass. For all other shade treatments, Sea Isle 2000, Celebration, and Tifway
performed similarly. However, Diamond had ~0.93 and ~4.3 unit lateral spread increases
144
than both bermudagrass cultivars when grown under yellow and black shade,
respectively.
Shoot Width
Shade treatments did not impact turfgrasses shoot width at week 4 (Table 8.5).
Also, few differences were noted at week 4 between turfgrasses shoot width. However,
black shade-grown Sea Isle 2000 (23%), Celebration (29%), and Tifway (36%) had shoot
width reductions compared to Diamond. Diamond and Sea Isle 2000 shoot width was not
impacted by shade at week 8. Celebration grown under black shade reduced shoot width
38% and 25% compared to red and blue shade, respectively. For Tifway, yellow shade
showed the least impact (11% reduction) on shoot width relative to full-sunlight, while
other shade treatments averaged a 29% shoot width reduction relative to full-sunlight.
No differences were noted between turfgrasses shoot width by week 8.
Chlorophyll
By week 3, all turfgrasses showed chlorophyll concentration declines relative to
full-sunlight (Table 8.6). Diamond grown under blue shade had 46% and 32%
chlorophyll increase compared to yellow and red shade. Sea Isle 2000 grown under blue
and black shade had 20% and 33% lower chlorophyll concentration, respectively,
compared to yellow shade. When grown under black shade, Celebration and Tifway
chlorophyll concentrations were ~30% and 59% lower, respectively, than when grown
under yellow, red, and blue shade. Diamond grown under yellow shade had ~37% less
chlorophyll than yellow shade-grown Sea Isle 2000, Celebration, and Tifway.
145
Table 8.5. Relative shoot width of 'Diamond' zoysiagrass, 'Sea Isle 2000'
seashore paspalum, 'Celebration' bermudagrass, and 'Tifway' bermudagrass
affected by full-sunlight and various types of filtered light (~65% reduction)
in a greenhouse study.
-----------------------------------------Week 4---------------------------------
Treatment Diamond Sea Isle 2000 Celebration Tifway LSD
Yellow† 88.4 84.3 90.3 77.7 NS
Red 87.7 104.4 136.8 75.4 NS
Blue 84.7 72.3 82.3 65.3 NS
Black 100.1 81.2 77.4 73.4 17.12‡
LSD NS NS NS NS
-----------------------------------------Week 8---------------------------------
Yellow 86.8 84.9 72.4 89.2 NS
Red 89.8 82.3 84.6 75.5 NS
Blue 83.3 76.5 76.6 72.3 NS
Black 81.3 73.9 61.5 65.9 NS
LSD NS NS 12.89§ 12.82
†Yellow: filters <520 nm, Red: filters <560nm, Blue: filters >560, and Black:
filters all wavelengths. ‡Values within a row within each week followed by the same letter are not
significantly different at P≤0.05 by protected LSD. §Values within a column within each week followed by the same letter are not
significantly different at P≤0.05 by protected LSD.
LSD = least significant difference, NS = not significant.
However, Diamond produced ~27% greater chlorophyll than Sea Isle 2000 and
Tifway when grown under blue shade. Under black shade, Sea Isle 2000 and Celebration
produced ~31% greater chlorophyll than Tifway.
Few chlorophyll differences were noted among turfgrasses by week 6 (Table 8.6).
However, black shade reduced Tifway chlorophyll concentration 43%, 34%, and 13%
compared to yellow, red, and blue shade, respectively. Also, Diamond had 49%, 57%,
and 80% greater chlorophyll than Sea Isle 2000, Celebration, and Tifway, respectively.
146
Table 8.6. Relative shoot chlorophyll concentration of 'Diamond' zoysiagrass, 'Sea
Isle 2000' seashore paspalum, 'Celebration' bermudagrass, and 'Tifway'
bermudagrass affected by full-sunlight and various types of filtered light (~65%
reduction) in a greenhouse study.
----------------------------------------Week 3----------------------------------------
Treatment Diamond Sea Isle 2000 Celebration Tifway LSD
Yellow† 64.7 87.8 91.2 87.2 15.39
§
Red 71.2 77.0 85.9 78.3 NS
Blue 94.2 73.4 84.4 75.4 15.29
Black 81.7 66.0 66.9 50.6 14.75
LSD 17.94‡ 11.60 17.53 15.09
----------------------------------------Week 6----------------------------------------
Yellow 110.1 92.7 90.3 89.4 NS
Red 99.8 82.6 85.1 83.9 NS
Blue 100.1 80.2 87.4 79.1 NS
Black 112.1 75.3 71.6 62.4 28.11§
LSD NS NS NS 16.43‡
†Yellow: filters <520 nm, Red: filters <560nm, Blue: filters >560, and Black: filters all
wavelengths. ‡Values within a column followed by the same letter are not significantly different at
P≤0.05 by protected LSD.
§Values within a row followed by the same letter are not significantly different at P≤0.05
by protected LSD.
LSD = Least significant difference, NS = not significant.
Carbohydrates
Root TNC
Different shade types did not impact root TNC, however, full-sunlight provided
~10% increase in root TNC compared to other light treatments (Table 8.7). Sea Isle 2000
produced greatest root TNC (36.5 mg g-1
), while Diamond (34.1 mg g-1
) and Tifway
(33.8 mg g-1
) showed lowest root TNC values.
147
Table 8.7. Root and shoot total non-structural carbohydrates (mg g-1
) of
'Diamond' zoysiagrass, 'Sea Isle 2000' seashore paspalum, 'Celebration'
bermudagrass, and 'Tifway' bermudagrass affected by full-sunlight and
various types of filtered light (~65% reduction) in a greenhouse study.
Shoot TNC (mg g-1
)
Treatment Root TNC (mg g-1
) Week 4 Week 8
Sun† 37.4 55.6 59.4
Yellow 33.2 50.5 54.3
Red 34.8 48.3 54.6
Blue 33.8 49.0 50.9
Black 34.9 44.1 49.3
LSD 2.37‡ 4.95 4.57
Shoot TNC (mg g-1
)
Turfgrass Root TNC (mg g-1
) Week 4 Week 8
Diamond 34.1 48.6 54.6
Sea Isle 2000 36.5 47.7 57.5
Celebration 34.9 51.1 51.4
Tifway 33.8 50.7 51.3
LSD 2.12‡ NS 4.09
†Sun: full sunlight control, Yellow: filters <520 nm, Red: filters <560nm, Blue:
filters >560, and Black: filters all wavelengths. ‡Values within a column followed by the same letter are not significantly different
at P≤0.05 by protected LSD.
LSD = Least significant difference, NS = not significant.
Shoot TNC
Full sunlight showed ~16% and ~14% greater shoot TNC at week 4 and 8,
respectively, compared to other light treatments (Table 8.7). At week 4, yellow shade
had 15% greater shoot TNC than black shade, while yellow and red shade had ~11%
greater shoot TNC than black shade by week 8. Turfgrass shoot TNC differences were
not detected at week 4, however, at week 8, Sea Isle 2000 had ~12% greater shoot TNC
than Tifway and Celebration.
148
Specific Root Length and Root Length Density
Diamond and Celebration produced similar SRL, while Tifway bermudagrass
showed ~101% SRL increase compared to Sea Isle 2000 (Table 8.7). Compared to shade
treatments, full-sunlight showed lowest (8.4 cm mg-1
) SRL. Under different types of
light, blue shade had ~48% SRL increase compared to other shade treatments.
Under different types of shade, no RLD differences were noted between
turfgrasses (Table 8.8). However, different light environments impacted RLD for each
turfgrass, except Celebration. Red shade produced a 1.6 and 1.1 unit RLD increase
compared to blue and black shade for Diamond, respectively. Similarly, Sea Isle 2000
grown under red shade had a RLD increase of 24% and 35% compared to blue and black
shade, respectively. However, RLD for Tifway grown under blue shade showed a 3.2
and 2.8 unit decrease compared to yellow and red shade, respectively.
Root Biomass
In response to different types of light, only Diamond showed significant
variations (Table 8.8). Diamond grown under red shade produced 3.6 and 1.5 unit root
biomass increases compared to blue and black shade, respectively. Under yellow and red
shade, Diamond and Sea Isle 2000 performed similarly, while Celebration and Tifway
showed no significant differences. However, Sea Isle 2000 had 1.9 and 4.7 unit root
biomass increases compared to Diamond and Tifway, respectively, when grown under
blue shade.
149
Table 8.8. Total root biomass and root length density of ‘Diamond'
zoysiagrass, 'Sea Isle 2000' seashore paspalum, 'Celebration'
bermudagrass, and 'Tifway' bermudagrass affected by full-sunlight and
various types of filtered light (~65% reduction) in a greenhouse study.
Root Biomass
------------------------------------Week 8----------------------------------
Treatment Diamond Sea Isle 2000 Celebration Tifway LSD
Yellow 54 45 21 22 20.9§
Red 64 48 22 13 35.1
Blue 14 40 27 7 23.5
Black 26 25 12 14 NS
LSD 37.0‡ NS NS NS
Root Length Density
------------------------------------Week 8----------------------------------
Yellow 65.7 46.1 37.9 82.9 NS
Red 82.4 48.8 38.2 76.6 NS
Blue 31.6 39.3 35.8 19.9 NS
Black 38.7 36.1 18.4 36.7 NS
LSD 37.81‡ 9.34 NS 51.38
†Sun: full sunlight control, Yellow: filters <520 nm, Red: filters <560nm, Blue:
filters >560, and Black: filters all wavelengths. ‡Values within a column followed by the same letter are not significantly
different at P≤0.05 by protected LSD.
§Values within a row followed by the same letter are not significantly different
at P≤0.05 by protected LSD.
LSD = Least significant difference, NS = not significant.
Discussion
Few previous reports have investigated the morphological and physiological
responses of warm-season turfgrasses to different light spectral qualities. Also, Diamond,
Sea Isle 2000, and Celebration are turfgrasses gaining popularity, however, direct
comparisons of their performance in full-sunlight and shade compared to industry
standards have not been reported. In this study, under full-sunlight and shade, turfgrasses
performance significantly varied. Diamond zoysiagrass was the most shade-tolerant
150
turfgrass species among selected turfgrasses. Diamond zoysiagrass TQ scores were
consistently higher, chlorophyll concentration decreases compared to full-sunlight were
minimal, and lateral spread growth was least impacted by shade compared to other
turfgrasses. Bunnell et al. (2005c) also indicated zoysiagrass was more shade-tolerant
than two bermudagrass cultivars. Also, Diamond zoysiagrass maintains acceptable TQ
scores under 75% to 81% shade (Qian et al., 1998; Qian and Engelke, 1999). Previous
studies have also indicated that seashore paspalum cultivars are more shade tolerant than
bermudagrass cultivars, „TifSport‟ and TifEagle (Jiang et al., 2004 and 2005). Similar
results were noted in this study as Sea Isle 2000 consistently outperformed Tifway in
shade, however, data collected indicates that Celebration possesses a similar shade
tolerance to Sea Isle 2000. Regardless, both cultivars TQ scores were below 6 by week 8
of shade stress.
Previous reports have indicated Celebration bermudagrass is more shade tolerant
than Tifway bermudagrass (Bunnell et al., 2005c; Baldwin et al., 2008). While plants
have evolved many adaptive mechanisms in order to adapt to natural variations in the
environment, including photosynthesis, these adaptive changes are currently unknown
regarding bermudagrass shade tolerance. A reason for this enhanced shade adaptation
appears to be a morphological advantage exhibited by Celebration. Typically, inhibited
lateral stem growth negatively impacts warm-season turfgrass development when
sunlight is intercepted (Beard, 1997). Also, a shaded cool-season turfgrass, tall fescue
(Festuca arundinacea Schreb.), shifted biomass production from roots to shoots, which
led to thinner and less dense leaf blades compared to full-sunlight (Allard et al., 1991).
151
In this study, under full-sunlight, Celebration clipping yield production was consistently
lower than Tifway, while Celebration lateral spread was greater than Tifway. Similar
trends were noted under shade. Karcher et al. (2005a) reported similar results as
Celebration recovery from divot stress was quicker than Tifway bermudagrass. Clipping
yield and lateral spread data indicates Celebration minimizes vertical shoot growth and
continues energy constituent allocation for continued lateral shoot growth production
under shade. This plastic, morphological adaptation could possibly be due to plant
hormone manipulation, in particular, gibberellic acid (GA), photoreceptor activity
(phytochrome/chromophore), anatomical alterations, or efficient sun-fleck utilization.
All of these possibilities would lead to increased carbon dioxide (CO2) fixation capacity
at reduced light intensities.
Boardman (1977) indicated shade plants can increase solar energy collection
efficiently by altering chloroplast arrangement. Few published reports compare shade-
sensitive and shade-tolerant turfgrass cultivars anatomical development when grown
under shade. Wilkinson and Beard (1975) reported shade-tolerant „Pennlawn‟ red fescue
(Festuca rubra L.) grown under shade developed a thicker cuticle layer, enhanced
vascular support tissue, and maintained a distinct chloroplast structure compared to shade
sensitive „Merion‟ Kentucky bluegrass (Poa pratensis L.). However, Wherley et al.
(2005) noted few anatomical differences between shade-tolerant and shade-sensitive tall
fescue cultivars grown under shade. Future studies investigating the anatomical
development of Celebration may provide clues to its apparent relative shade-tolerance.
152
Efficient conversion of short bursts of solar energy (sun-flecks) into carbohydrate
production supporting lateral stem growth may also enhance Celebration‟s relative shade-
tolerance. The unique anatomical organization of C4 plants typically enhances adaptation
to warm and dry climatic regions because CO2 levels remain elevated near ribulose
bisphosphate carboxylase/oxygenase (Rubisco). However, this unique anatiomical
organization may reduce C4 plants ability to adapt to variable environments, such as low
light, because C4 photosynthesis requires coordinated changes between mesophyll and
bundle sheath tissues (Sage and McKown, 2006). Specifically, C4 plants can not readily
adapt to sunflecks (typically occur in heavily shaded environments) due to distance
between mesophyll CO2 fixation reactions and bundle sheath Calvin cycle metabolites
(Horton and Neufeld, 1998). Future studies determining the importance of sun-fleck
contribution to C4 turfgrass photosynthesis is warranted.
The impact of light quality on turfgrass growth and development remains poorly
understood. In other plant disciplines, spectral shade results in greater individual leaf
area and plant biomass compared to neutral shade (typically used in turfgrass research)
(Stuefer and Huber, 1998). Increased overall above-ground biomass for shade-sensitive
turfgrasses is detrimental due increased tissue removal from mowing. Overall, in this
study, yellow and red shade performed similarly, closely followed by blue shade. Shade
provided by the black cloth consistently resulted in poorest performance of all
turfgrasses.
Compared to blue shade, yellow shade on several occasions produced greater
clipping yield (i.e. plant height), while red shade produced similar clipping yield data for
153
most turfgrasses. Chlorophyll concentrations remained similar between different types of
light, however Diamond grown under blue shade produced 32% and 46% (week 3)
greater chlorophyll than red shade. Similar results have been noted in other studies. In
chrysanthemums (Dendranthema grandiflorum) plants, filtering wavelengths <500 nm
produced tallest plants (Khattak and Pearson, 2006). Poudel et al. (2008) noted grape
(Vitis spp.) genotypes grown under ~600 - 680 nm light had lowest chlorophyll content,
but greatest plant height compared to ~430 - 510 nm light. Similarly, Lee et al. (2007)
determined light with a peak emission of 440 nm produced 54% greater chlorophyll, but
8% less plant dry weight than light with a peak emission of 650 nm for Ashwagandha
(Withania somnifera (L.) Dunal.). In another study, lettuce genotypes (Lactuca Sativa
L.) shoot production under red light was 3.8 units greater than blue light exposure
(Hunter and Burritt, 2004). Kim et al. (2004) reported that chrysanthemums exposed to
650 nm light produced 40% greater plant dry weight than 440 nm light grown plants.
However, chlorophyll concentrations were not impacted by either type of light. McVey
et al. (1969) also reported blue shade resulted in reduced shoot biomass production.
Khattak and Pearson (2006) noted the number of chrysanthemums stomata were greater
under blue shade compared to red shade. This may indicate light with shorter
wavelengths (i.e. blue light) may play a significant role in plant photosynthesis.
154
Conclusion
In summary, this study has demonstrated that both quantity and quality of light
impacts growth and development of various turfgrass species. Also, turfgrass species
growth responses varied under reduced light. Overall, black shade most negatively
inhibited parameters measured followed by blue shade, while yellow and red shade
performed similarly. For turfgrasses, Diamond was the most shade-tolerant, while
Tifway was the most shade-sensitive. Celebration and Sea Isle 2000 performed similarly.
Future studies continuing light quality research for other warm-season turfgrass cultivars
needs to be initiated, as well as field studies confirming these greenhouse results. Also,
this study did not take into account the impact of the R:FR ratio, which could potentially
alter results. This study implies different types of shade significantly impact the
performance of warm-season turfgrasses.
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CHAPTER IX
CREEPING BENTGRASS SEASONAL RESPONSES TO VARIOUS WINTER LIGHT
INTENSITIES
Introduction
Creeping bentgrass (Agrostis stolonifera var. palustris (Huds.)), a C3 plant, has
been widely used as a putting green turfgrass in cooler climate areas and the transition
zone (McCarty et al., 2005). However, due to seasonal temperature variation in the
transition zone, creeping bentgrass putting greens face many stresses and agronomic
challenges year round, including shade. Cool-season turfgrass decline in severe shade is
mainly attributed to increased disease pressure (Beard, 1965; Beard 1969; Vargas and
Beard, 1981), partially because tree water transpiration is greatest at night extending dew
duration (Dudeck and Peacock, 1992; Williams et al., 1996, 1998). Current management
strategies to combat shade stress include raising height of cut (White, 2004; Bunnell et
al., 2005b), reducing nitrogen (N) input (Burton et al., 1959; Bell and Danneberger,
1999b; Goss et al., 2002; Bunnell et al., 2005b;), applying plant growth regulators
(PGRs) (Qian et al., 1998; Qian and Engelke, 1999; Stier and Rogers, 2001; Ervin et al.,
2004; Bunnell et al., 2005b), and watering deeply and infrequently (Dudeck and Peacock,
1992).
Trinexapac-ethyl (TE, Primo Maxx, Syngenta Chem Co., Greensboro, NC)
effectively inhibits gibberellic acid (GA) production (Adams et al., 1992) late in the
mevalonic acid pathway suppressing shoot vertical growth. In Kentucky bluegrass (Poa
156
pratensis L.) cultivars, TE (0.048 kg a.i. ha-1
) reduced GA1 49% and increased GA20
146% when grown in 87% shade (Tan and Qian, 2003). Due to GA disruption, TE
enhances warm-season and cool-season turfgrass response when light interception is
interrupted.
„Penncross‟ creeping bentgrass grown in 80% shade treated with multiple TE
applications at 0.042 and 0.070 kg a.i. ha-1
increased fructose concentration ~39% with
minimal effects on other carbohydrate constituents (Goss et al., 2002). Similarly, Steinke
and Stier (2003) noted monthly and bimonthly TE applications enhanced Penncross
creeping bentgrass TQ and chlorophyll concentration in 80% shade. It appears consistent
TE applications is an effective management strategy to reduce shade damage. However,
Gardner and Wherley (2005) noted a TQ decline for tall fescue (Festuca arundinacea
Schreb. „Plantation‟), rough bluegrass (Poa trivialis L.), and sheep fescue (Festuca ovina
L.) and turfgrass density decline in tall fescue and rough bluegrass grown under Acer
saccharinum L. and Platanus occidentalis L. trees (91% light reduction) four to six
weeks after TE (0.29 kg a.i. ha-1
) applications.
While morning shade is perceived more detrimental than afternoon shade for
warm- and cool-season turfgrass growth, few experiments have investigated this
observation. Bell and Danneberger (1999a) noted shade duration was more detrimental
than morning or afternoon shade for Penncross creeping bentgrass. However, a warm-
season species, „TifEagle‟ bermudagrass (Cynodon dactylon (L.) Pers. X C.
transvaalensis), declined more readily in the absence of afternoon solar irradiance
(Bunnell et al., 2005a).
157
In the transition zone, creeping bentgrass putting greens often experience summer
decline due to a combination of stresses, which include elevated soil CO2 levels (Bunnell
et al., 2002; Rodriguez et al., 2005), high soil temperatures (Xu and Huang, 2000; Xu and
Huang, 2001), and increased day and night temperatures (Huang and Gao, 2000; Fu and
Huang, 2003). Management practices to combat these stresses are well documented
(Dernoedon, 2000; Feng et al., 2002; Liu and Huang, 2003; Bunnell et al., 2004; Guertal
et al., 2005). Winter shade is potentially very damaging due to shorter photoperiods,
reduced light intensities, solar elevation angles, and extended frost accumulation.
However, winter shade impacts on creeping bentgrass putting greens and management
recommendations to minimize winter shade stress have yet to be investigated. Also,
winter shade effects on spring and summer performance are lacking. Therefore, research
objectives of this study included evaluating winter shade impacts on the performance of
„L93‟ creeping bentgrass, responses of L93 creeping bentgrass under morning or
afternoon shade, effects of winter month shade on spring and summer performance, and
TE as a management tool to reduce winter shade stress.
Materials and Methods
This research was conducted at the Turfgrass Research Center, Clemson
University, Clemson, SC on L93 creeping bentgrass field research plots established in
August, 2002 with soil profile constructed to approximate United States Golf Association
(USGA) recommendations (USGA, 1993). Shade treatments were initiated 1 December
2004 and terminated 28 February 2005 and repeated the subsequent winter. Data
158
collection continued through July each year to determine any deleterious effects that
continuous, morning, or afternoon winter shade had on spring and summer bentgrass
performance. Light treatments consisted of control (no shade), 55%, and 95% (Table 1)
light reductions using a neutral density, polyfiber black shade cloth (Glenn Harp and
Sons, Inc., Tucker, GA) supported by polyvinyl chloride (PVC) 183 cm in length and 152
cm in width with 2.54 cm diameter PVC pipes. Shade structures were placed 15 cm
above the bentgrass surface to reduce early morning and late afternoon sunlight
encroachment, yet maintain adequate wind movement. For morning shade, tents were
placed on the bentgrass surface at sunrise and removed at solar noon. For afternoon
shade, tents were placed on the bentgrass surface at solar noon and removed at sunset.
For full-day shade, tents were placed on the bentgrass surface at sunrise and removed at
sunset. Regardless of shade treatment, all tents were removed nightly.
Trinexapac-ethyl was applied at 0.02 kg ha-1
using the emulsifiable concentrate
(11.3% a.i.) using a CO2–pressurized backpack sprayer beginning on 1 December and
every two weeks through 31 July each year. The bentgrass green was mowed at 3.2 mm
height two to four times weekly during winter depending on weather conditions with
clippings removed. During spring, summer, and fall, mowing (3.2 mm) occurred six to
seven times weekly. A combination of 10N-1.3P-4.2K and 5N-0P-5.8K liquid fertilizers
(Progressive Turf, LLC., Ball Ground, GA) were applied early January 2005 and 2006 at
a rate of 4.9 kg N ha-1
. In spring, a rate of 9.7 kg N ha-1
was applied every two weeks
using Progressive Turf liquid fertilizer, while in summer, same liquid fertilizer (10-1.3P-
4.2K and 5-0P-5.8K) was applied at a rate of 4.9 kg N ha-1
every two weeks. In fall, N
159
was applied every two weeks at a rate of 9.7 kg ha-1
using liquid fertilizers (10N-1.3P-
4.2K and 5N-0P-5.8K). Hollow tine aerification (1.3 cm diam. tines 10 cm in length with
5.0 cm spacing) occurred twice in the spring and once in the fall. Following cultivation,
a rate of 24.4 kg N ha-1
using 18N-1.3P-14.9K greens grade granular fertilizer
(Anderson‟s, Maumee, OH) was applied. Disease occurrence in winter was minimal,
therefore no fungicides were applied. In summer, chlorothalonil (Daconil) (11.8 L ha-1
),
azoxystrobin (Heritage) (48 kg a.i. ha-1
), and mefonoxam (Subdue MAXX) (6.4 L ha-1
)
were applied as needed for dollar spot (Sclerotinia homoeocarpa F.T. Bennet), pythium
(Pythium spp.), and brown patch (Rhizoctonia solani Kuhn.) management. The bentgrass
green did not receive any topdressing, except following aerifications.
Data collection
Data collected included microenvironment conditions, visual turfgrass quality
(TQ), clipping yield, shoot chlorophyll concentration, total root biomass, and root total
non-structural carbohydrates (TNC).
Microenvironment parameters included surface and soil temperature, wind
movement, and light quality and quantity. Surface and soil temperature was recorded
four times weekly during winter months at solar noon for one full-sun treatment, under
one 55% and one 95% shade cloth using an indoor/outdoor thermometer (model #1455
and model #9840, Taylor, Oakbrook, IL). Sensors for surface temperature were placed
on the surface, while soil temperatures were recorded at a 7.6 cm depth. Wind movement
was recorded twice on days with a consistent breeze using an anemometer (model #CS-
800, Clark Solutions, Hudson, MA). Light quality was measured on a clear, cloudless
160
day at solar noon using a spectroradiameter (Model LI-1800; LiCor, Inc., Lincoln, NE),
while photon flux density ( mol m-2
s-1
) was recorded four times weekly during winter
months at solar noon for one full-sun treatment, under one 55% and one 95% shade cloth
using a quantum radiometer (Model LI-250, LiCor, Lincoln, NE).
Visual TQ ratings were measured monthly based on color, density, texture, and
uniformity of the L93 creeping bentgrass surface. Quality was visually evaluated from 1
to 9, 1 = brown, dead turf, 6 = minimal acceptable turf, 9 = ideal green, healthy turf.
Clipping yield (g m-2
) was collected mid-January, late-February, and mid-May for
both years. Shoot tissue was collected using a walk behind greens mower
(Greenmaster® 800, The Toro Company, Bloomington, MN) following three days of
growth. Clippings were oven dried at 80oC for 48 hr and weighed to quantify shoot
production.
Shoot chlorophyll (mg g-1
) was determined on same dates as clipping yield. Fresh
clippings were collected (as described above) from each plot and immediately placed in a
plastic bag inside a covered bucket to prevent sunlight degradation. Clippings were
weighed (0.1g) and placed in a glass test tube (1.0 cm in width and 14.8 cm in length)
with 10 mL of dimethyl sulfoxide (DMSO), which eliminates shoot tissue grinding to
extract chlorophyll (Hiscox and Israelstam, 1979). Samples were incubated in 65 oC
water on a hot plate (PC-600, Corning, Corning, NY) for 1.5 hr and continuously shaken.
Upon completion, samples were passed through filter paper (Whatman 41, Whatman,
England) and remaining extract (2 mL) transferred into cuvettes. Absorbance values
were recorded at 663 nm and 645 nm wavelengths using a spectrophotometer (GenesysTM
161
20, ThermoSpectronic, Rochester, NY). Blanks were initially run and also after every
sixth sample. The following formula was used to calculate total shoot chlorophyll: (mg
g-1
) = (8.02 * D663 + 20.2 * D645) * 0.1 (Arnon, 1949).
Roots were extracted from the soil using a cylinder core sampler (7.5 cm in diam.
by 30 cm deep) 15 January and 28 February for both years to determine total root
biomass. One plug was randomly sampled from each plot and re-filled with 85:15 sand:
peat. For all future parameters, the old plug site was ignored. Once all soil was
completely removed from each soil plug using tap water, roots were clipped from shoot
tissue base and placed in an oven (80.0 oC) for 48 hr, then weighed.
Root TNC (mg g-1
) was collected end of February for both years. Root tissue was
harvested using a bulk density sampler which extracted 154.4 cm3 (10.2 cm in depth)
cores prior to sunrise to minimize any diurnal fluctuations. Following soil removal, root
tissue samples were stored at -75oC until freeze dried at -40
oC for two wks to cease all
metabolic activity. Samples were then ground using an A-10 plant grinder (IKA Works,
Inc., Wilmington, NC). Grounded samples were rehydrated with 100 L of 80% ethanol
(EtOH) and 2 mL of 0.1 M sodium acetate buffer (pH 4.5) in glass test tubes 13 X 100
mm. Rehydrated samples were placed in boiling water for 1 hr, cooled for 1 hr and
repeated. Then, 2 mL of invertase (Sigma I-4753, 433 units mg-1
) and amyloglucosidase
(Sigma A-7255, 23,000 units g-1
) were added to solution. Samples were placed in water
bath (40 – 45oC) for three days and vortexed three times daily. TNC analysis was
analyzed using Nelson‟s Assay (1944), which determines glucose and fructose in plant
tissue (Nelson, 1944; Somogyi, 1945). A 25 L of aliquot was removed and two
162
reagents (copper and arsenomolybdate) were added to the solution. Absorbance values
were measured at 520 nm using a spectrophotometer.
Data Analysis
Treatment factors were arranged in a split-block design with four replications.
Treatment effects were evaluated using analysis of variance within SAS (version 9.1,
SAS Institute, Cary, NC). No treatment by TE interactions occurred for any parameters;
therefore, marginal means for light treatments and TE were examined separately. For TQ
scores, year by treatment interactions occurred for January, February, and March,
therefore yearly results are presented separately. For chlorophyll and clipping yield, year
by treatment interactions occurred for January, therefore yearly results are presented
separately. All other parameters showed no significant treatment by year interactions,
therefore, yearly data were pooled. Means separation was performed using Fisher‟s
protected least significant difference (LSD) test with = 0.05.
Results
Microenvironment
Shade significantly altered the microenvironment for each treatment (Table 9.1).
The 55% and 95% shade cloths reduced light intensity 58% and 96% compared to full-
sunlight. Within each month, 95% full day shade significantly reduced surface
temperatures ~57% compared to full-sunlight. In December and February, 95% full day
163
Table 9.1. Winter surface and soil temperatures (oC) and percent light reduction
recorded at solar noon four times weekly from 1 December to 28 February in year I and
II.
Surface and soil temperature (oC)
Light intensity
( mol m-2
s-1
)
Treatment December January February December to
February
Surface Soil Surface Soil Surface Soil
FS
† 17.3 5.7 20.8 8.4 22.8 8.5 338.2
55FD 13.2 4.3 16.7 7.3 18.0 6.9 143.2
95FD 10.8 3.9 14.0 6.8 14.1 6.1 12.6
LSD 2.25
‡ 1.32 2.54 1.65 3.17 1.80 29.07
†Abbreviations: FS=full-sunlight, 55FD=55% full day shade, 95FD=95% full day shade.
‡Values within a column followed by the same letter are not significantly different at P≤0.05
by protected LSD.
shade treatment soil temperatures were ~43% lower than full-sunlight. Also, coldest
surface and soil temperatures occurred in December, followed by a gradual warming
trend from January to February. Light quality and wind speed were not affected by shade
cloths and structures (data not shown).
Turfgrass Quality
One month following shade treatment initiation, significant differences were
noted between treatments (Table 9.2). In December, full-day 95% shade produced
highest TQ (7.4) compared to all other treatments, however, this response was transient in
year I. In year I, by January (4.9) and February (4.2), full-day 95% shade showed lowest
TQ scores compared to all other treatments. No differences were detected between
164
Table 9.2. Turfgrass quality of 'L93' creeping bentgrass in December, January,
and February in response to full-sunlight and 55% and 95% morning,
afternoon, and full-day winter shade (December to February, 2004 to 2006) and
trinexapac-ethyl (0.02 kg ha-1
) applications every two weeks from 1 December to
31 July, 2004 to 2006.
-----------------Turfgrass Quality†-------------
Light Duration
Trinexapac-
ethyl (TE) December January February
Year
1
Year
II
Year
1
Year
II
Full-
sunlight
-- 5.7 6.8 5.2 5.5 5.1
55%
shade Morning -- 6.3 6.7 5.5 6.2 5.3
Afternoon -- 6.5 7.3 5.7 6.6 5.4
Full-day -- 6.7 6.8 6.4 6.0 6.3
95%
shade Morning -- 6.7 6.7 6.1 6.0 6.1
Afternoon -- 6.8 6.8 6.1 6.6 5.9
Full-day -- 7.4 4.9 6.8 4.2 6.3
---------------------------LSD---------------------
0.40‡ 0.57 0.56 0.55 0.59
TE 6.6 6.5 5.9 5.5 5.5
No TE 6.5 6.6 6.1 6.2 6.0
---------------------------LSD---------------------
NS NS NS 0.29‡ 0.31
†Turfgrass quality based on a scale of 1-9, 1=brown/dead turfgrass, 6=minimally
acceptable turfgrass, 9=healthy/green turfgrass. ‡Values within a column followed by the same letter are not significantly
different at P≤0.05 by protected LSD.
LSD, least significant difference, NS = not significant.
morning and afternoon shade in December. Afternoon shade (55%) showed a 0.6 unit
TQ increase compared to morning shade (55%), however, this difference was not
detected in January, 2006 or in February for either year. Differences were not detected
between full-day and diurnal 55% shade in January, 2005, however afternoon 55% shade
165
increased TQ 0.6 units compared to full-day 55% shade. In January, 2005, morning and
afternoon shade (95%) had a ~1.9 unit TQ increase compared to full-day 95% shade.
Similarly, in February, 2006, full-day 95% shade reduced TQ by ~2.1 units compared to
morning and afternoon 95% shade.
Unlike year I, in 2006, full-day 95% shade remained above the acceptable TQ
threshold of 6 through January and February (Table 9.2). No differences were detected
between morning or afternoon shade for either shade intensity. However, full-day 55%
shade increased TQ ~0.8 and ~1.0 units compared to morning or afternoon 55% shade.
When grown under full-day 95% shade, bentgrass TQ increased 0.7 units compared to
95% morning or afternoon shade.
Trinexapac-ethyl applications every 2 wks did not impact TQ scores in December
or January (Table 9.2). However, TE-treated plots in February, 2005 and 2006 showed a
0.7 and 0.5 unit TQ decrease, respectively, compared to non TE-treated plots.
In March, 2005, 95% afternoon shade increased TQ 0.8 units compared to
morning 95% shade, however, no morning or afternoon TQ variations were noted under
55% shade (Table 9.3). Regardless, full-day 95% shade produced lowest TQ (4.3)
compared to other treatments. Minimal winter sunlight negatively impacted spring or
summer TQ ratings. By April, regardless of winter shading, all plots had acceptable TQ.
Trinexapac-ethyl increased TQ by 0.6 and 0.2 units in May and June, respectively,
compared to non TE-treated plots.
166
Table 9.3. Turfgrass quality of 'L93' creeping bentgrass in spring and summer in
response to full-sunlight and 55% and 95% morning, afternoon, and full-day
winter shade (December to February, 2004 to 2006) and trinexapac-ethyl (0.02
kg ha-1
) applications every two weeks from 1 December to 31 July, 2004 to 2006.
-------------------Turfgrass Quality†-----------
Light Duration
Trinexapac-
ethyl (TE) March April May June July
Year
1
Year
II
Full-
sunlight
-- 5.3 5.5 6.7 7.1 7.5 6.6
55%
shade Morning -- 5.7 6.0 6.8 7.1 7.6 6.4
Afternoon -- 5.8 6.2 7.1 7.5 7.8 6.2
Full-day -- 5.5 6.4 6.8 7.4 7.5 6.5
95%
shade Morning -- 5.3 6.0 6.7 7.2 7.4 6.2
Afternoon -- 6.1 6.1 7.0 7.2 7.4 6.6
Full-day -- 4.3 6.3 6.9 6.9 7.5 6.6
-----------------------------LSD----------------------- 0.64
‡ NS NS 0.40 0.15 0.27
TE 5.5 5.9 6.9 7.5 7.6 6.4
No TE 5.5 6.2 6.7 6.9 7.4 6.4
-----------------------------LSD----------------------- NS 0.29
‡ NS 0.21 0.08 NS
†Turfgrass quality based on a scale of 1-9, 1=brown/dead turfgrass, 6=minimally
acceptable turfgrass, 9=healthy/green turfgrass. ‡Values within a column followed by the same letter are not significantly different at
P≤0.05 by protected LSD. LSD, least significant difference, NS
= not significant.
Chlorophyll
In January, 2005, 55% afternoon shade produced greatest chlorophyll
concentration (3.0 mg g-1
), however, in year II, 95% full-day shade produced greatest
chlorophyll concentration (2.2 mg g-1
) (Table 9.4). No differences were detected
167
Table 9.4. Chlorophyll concentration (mg g-1
) of 'L93' creeping bentgrass in
January, February, and May in response to full-sunlight and 55% and 95%
morning, afternoon, and full-day winter shade (December to February, 2004 to
2006) and trinexapac-ethyl (0.02 kg ha-1
) applications every two weeks from 1
December to 31 July, 2004 to 2006.
-----------Chlorophyll (mg g-1
)-------
Light Duration
Trinexapac-ethyl
(TE) January February May
Year
1
Year
II
Full-
sunlight
-- 2.5 1.5 2.0 2.4
55% shade Morning -- 2.4 1.6 2.1 2.4
Afternoon -- 3.0 1.6 2.1 2.5
Full-day -- 2.7 1.7 2.2 2.3
95% shade Morning -- 2.5 1.8 2.2 2.4
Afternoon -- 2.6 1.8 2.3 2.4
Full-day -- 2.5 2.2 2.5 2.5
---------------------LSD------------------- 0.64
† 0.20 0.16 NS
TE 2.5 1.7 2.1 2.5
No TE 2.6 1.8 2.2 2.3
---------------------LSD------------------- NS NS 0.08
† NS
† Values within a column followed by the same letter are not significantly different
at P≤0.05 by protected LSD.
LSD, least significant difference, NS = not significant.
between 95% shade treatments in year I, while morning or afternoon shade did not
impact chlorophyll concentration in January, 2006. In February, full-day 95% shade
enhanced chlorophyll 25%, ~17%, and ~12% compared to full-sunlight, 55% shade
treatments, and 95% shade treatments. Meanwhile, morning or afternoon shade did not
influence chlorophyll concentrations. Also, chlorophyll differences were not detected in
168
May. Trinexapac-ethyl had minimal impacts on winter and spring chlorophyll
concentrations. In February, non TE-treated bentgrass minimally increased chlorophyll
concentration 5% compared to TE-treated plots.
Clipping Yield
Full-day 95% shade increased shoot growth 1.5 units compared to full-sunlight in
January, 2005 (Table 9.5). Also, morning shade (55%) decreased shoot growth 78%
compared to afternoon shade (55%). Clipping yield differences were not detected in
January, 2006. In February, clipping yield production increased 47% for bentgrass when
grown under 95% full-day shade compared to full-sunlight. By May, no shoot biomass
variations were noted. Trinexapac-ethyl reduced shoot growth ~38%, 79%, and 51% in
January (2005 and 2006), February, and May, respectively compared to non TE-treated
plots.
Root Biomass and total nonstructural carbohydrates
In February, 2006, shade treatments, regardless of intensity or duration, had ~49%
reduction in root biomass compared to full-sunlight (Table 9.6). Morning shade (55%)
reduced root TNC 19% compared to afternoon shade, however, under 95% shade, a 20%
root TNC increase was noted for morning shade compared to afternoon shade. Also, full-
sunlight produced 27%, 32%, and 25% greater root TNC compared to full-day 55%
shade, 95% afternoon shade, and 95% full-day shade, respectively. Trinexapac-ethyl did
not impact root biomass or root TNC in the winter.
169
Table 9.5. Clipping yield (g m-2
) of 'L93' creeping bentgrass in January, February,
and May in response to full-sunlight and 55% and 95% morning, afternoon, and
full-day winter shade (December to February, 2004 to 2006) and trinexapac-ethyl
(0.02 kg ha-1
) applications every two weeks from 1 December to 31 July, 2005 to
2006.
----------Clipping Yield (g m
-2)------------
Light Duration
Trinexapac-
ethyl (TE) January February May
Year
1
Year
II
Full-
sunlight
-- 1.09 0.49 0.36 0.47
55% shade Morning -- 1.73 0.47 0.44 0.42
Afternoon -- 1.98 0.47 0.34 0.46
Full-day -- 1.89 0.43 0.33 0.45
95% shade Morning -- 1.37 0.52 0.35 0.43
Afternoon -- 2.44 0.47 0.39 0.46
Full-day -- 2.72 0.38 0.53 0.40
------------------------LSD----------------------
1.022† NS 0.156 NS
TE 1.56 0.39 0.28 0.35
No TE 2.23 0.52 0.50 0.53
------------------------LSD----------------------
0.546† 0.104 0.083 0.043
†Values within a column followed by the same letter are not significantly different at
P≤0.05 by protected LSD. LSD, least significant difference, NS = not
significant.
170
Table 9.6. Total root biomass (g m-2
) and root total nonstructural carbohydrates
(mg g-1
) of 'L93' creeping bentgrass in January and February in response to full-
sunlight and 55% and 95% morning, afternoon, and full-day winter shade and
trinexapac-ethyl (0.02 kg ha-1
) applications every two weeks from 1 December to
31 July, 2005 to 2006.
Root Biomass
(g m-2
)
Root TNC
(mg g-1
)
Light Duration
Trinexapac-
ethyl (TE) January February
February
Full-
sunlight
-- 0.79 0.89
52.6
55%
shade Morning -- 0.64 0.64
46.3
Afternoon -- 0.81 0.61
55.2
Full-day -- 0.76 0.66
41.5
95%
shade Morning -- 0.71 0.58
47.9
Afternoon -- 0.86 0.60
39.9
Full-day -- 0.61 0.51
41.9
--------------------------LSD-----------------------
NS 0.229† 6.79
TE 0.76 0.62
45.5
No TE 0.72 0.66
47.5
--------------------------LSD-----------------------
NS NS NS †Values within a column followed by the same letter are not significantly different at
P≤0.05 by protected LSD. LSD, least significant difference, NS = not significant.
Discussion
Spring is a period of accelerated growth and carbohydrate accumulation of
creeping bentgrass in the transition zone. Therefore, winter shade, which is largely
ignored in the turfgrass literature, was evaluated to determine if limiting light availability
during winter months would inhibit spring and subsequent summer performance. To the
171
author‟s knowledge, this if the first research project initiated to specifically investigate
the impact of winter shade on creeping bentgrass putting greens.
Results indicate moderate to heavy winter shade may not be a limiting growth
factor for creeping bentgrass putting greens in the transition zone. Contributing to
bentgrass shade tolerance is its low requirement for sunlight. Typically, C3 plants are
able to maintain an appropriate photosynthesis:respiration ratio, where photosynthesis
exceeds respiration, compared to C4 plants in low light environments (Wahid and Rasul,
2005), possibly due to distance between mesophyll and bundle sheath tissues (i.e.
anatomical organization) (Sage and McKown, 2006) or efficient sunfleck utilization
(Horton and Neufeld, 1998). Previous research indicates bentgrass performs well under
moderate shade stress. Goss et al. (2002) stated bentgrass showed minimal deleterious
effects under 60% shade, while 80% shade inhibited bentgrass growth and development.
Bell and Danneberger (1999a) also indicated Penncross creeping bentgrass maintained
acceptable color, density, and tissue mass when grown under 69% shade. Reid (1933)
indicated bentgrass grown under heavy shade had comparable light green color compared
to controls (full-sunlight), however, root growth was restricted. These studies were
conducted to coincide with spring season leaf growth and/or fall season leaf drop.
In this study, following three months of winter shade, regardless of intensity or
duration, shade treatments consistently showed greater TQ scores and chlorophyll
concentrations compared to full-sunlight plots. Evergreen plants photosynthetic rates
decline when temperatures cool, however, chlorophyll continues its light absorbing
properties (Verhoeven et al., 2005). Therefore, photoinhibition will occur unless the
172
xanthophyll cycle and/or antioxidant leaf enzymes are employed by the plant to minimize
the impact of excessive light accumulation (Deming-Adams and Adams, 1996). In this
study, it appears increasing shade intensity served as a photo-protective role under
apparent high light stress, thereby minimizing excess light accumulation in the light-
harvesting complexes, which ultimately produces reactive oxygen species. Limited
research examining the role of xanthophyll pigments in turfgrass exists. Bell and
Danneberger (1999a) noted in a field study that bentgrass decreased violaxanthin
concentration with increasing shade stress, while other pigment concentrations remained
constant. McElroy et al. (2006), in a greenhouse study, reported carotenoid (zeaxanthin,
antheraxanthin, violaxanthin, neo-xanthin, epoxy-lutein, and -carotene) concentrations
decreased as low light intensity duration increased. Both of these studies examined
carotenoid concentrations during favorable growing temperatures for bentgrass. Future
studies investigating xanthophyll activity of cool-season turfgrasses under winter shade is
warranted to further understand the relationship between winter shade stress and
bentgrass performance. Differences between 95% full-day shade in year I and II remains
unknown. Monthly maximum and minimum air temperatures and precipitation were
examined. Temperature and precipitation differences did not occur over this two-year
field study (data not shown), therefore, it appears this yearly fluctuation is independent of
temperature and/or moisture availability.
While TE typically enhances cool-season turfgrass in shade (Goss et al., 2002;
Steinke and Stier, 2003; Tegg and Lane, 2004), this study indicates TE applications every
two weeks during winter negatively impacted bentgrass growth and color. Bentgrass
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growth slowed due to cool winter temperatures, therefore, applying TE, a gibberellin
inhibiting PGR which slows growth, further reduced growth and discolored bentgrass.
Other studies on warm-season turfgrasses have noted surface discoloration and density
decrease if TE is applied during periods below an optimal growth temperature range
(Johnson, 1994; Fagerness and Yelverton, 2000; McCullough et al., 2006; McCullough et
al., 2007). Also, Gardner and Wherley (2005) reported TE applied every 6 wks
decreased visual TQ and density of cool-season turfgrasses under shade stress. Greater
intervals between winter TE applications or reduced rates may have been more
beneficial. Beasley et al. (2007) noted TE uptake was greatest when temperature were
warm, however, dissipation rate increased compared to cooler temperatures. Therefore,
during cool winter months, as TE efficacy is greatest, applying TE in two week intervals
in unnecessary and caused bentgrass discoloration. Weekly winter temperature
fluctuations in the transition zone are common, therefore, prudent use of TE to
temporarily slow shoot growth during winter when temperatures are forecasted to be
above average should further enhance bentgrass performance in shade by minimizing
excessive shoot growth. When temperatures are below average for an extended period,
TE use should be applied with caution. Once shade tents were removed and temperatures
were consistently warm, TE enhanced bentgrass performance in spring and summer.
Moderate winter shade seemed beneficial for parameters measured in this study;
however, long-term effects of 95% shade through spring and into summer may decrease
bentgrass visual quality. While TQ and shoot chlorophyll concentrations increased under
95% shade in February, 2006, root mass and root TNC declined compared to full-sunlight
174
in February. This indicates bentgrass re-allocated energy constituents and carbohydrate
reserves to shoot tissue to maintain winter green color and continued winter growth,
instead of conserving carbohydrates. This strategy would presumably be detrimental
(i.e., carbohydrate depletion) for sustaining a high quality putting green surface during
summer stress if 95% shade continued through the spring. However, Beard and Daniel
(1966) noted temperature reductions enhanced „Old Orchard‟ creeping bentgrass root
activity. Thus, partial spring and summer shade, which reduces surface and soil
temperatures, may improve creeping bentgrass survival in the hot, humid transition zone
by initiating new summer root growth, as long as a prudent disease control program is
initiated.
Trinexapac-ethyl did not impact root biomass. Fagerness and Yelverton (2000)
also reported year-round TE applications did not enhance bentgrass root biomass.
Similarly, McCullough et al. (2007) reported no differences in non TE-treated compared
to TE-treated bentgrass root growth following late-spring and summer TE applications.
While TE did not increase root TNC in this study, Ervin and Zhang (2007) reported
increases in bentgrass leaf carbohydrate content following sequential TE applications in a
greenhouse study. Goss et al. (2002) reported TE-treated creeping bentgrass increased
carbohydrate content under 80% shade stress compared to non TE-treated creeping
bentgrass. Also, Goss et al. (2002) observed significant increases in shoot carbohydrate
content compared to root carbohydrate content of bentgrass when grown under 80%
shade. In our study, sampling shoot tissue TNC may have been more appropriate than
root TNC regarding shade stress.
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Overall, morning or afternoon shade minimally impacted parameters measured.
Results agree with Bell and Danneberger (1999a) which stated shade duration rather than
diurnal shade was more detrimental to Penncross creeping bentgrass growth under 80%
or 100% shade. However, in this study, 55% and 95% diurnal shade differently impacted
parameters measured. For example, 55% morning shade reduced root TNC, while 95%
morning shade enhanced root TNC compared to afternoon shade. Bunnell et al. (2005)
noted afternoon shade decreased root carbohydrate content of TifEagle bermudagrass
compared to morning shade. However, Bell and Danneberger (1999) did not detect any
bentgrass carbohydrate content variation in response to diurnal shade. It appears time of
shade may be more critical for bermudagrass putting greens, rather than cool-season
putting greens. Future research of other turfgrass species and cultivars response to
morning or afternoon shade would prove beneficial.
Conclusion
In summary, intensity of shade enhanced bentgrass growth, while duration of
winter shade had minimal impacts during winter. Regardless of winter stress, all plots
fully recovered by early spring as TQ scores were above the acceptable threshold of 6.
Future studies should investigate bentgrass performance with continued moderate shade
stress throughout spring and summer. Also, other bentgrass cultivars, as well as other
cool-season turfgrass species winter shade performance should be evaluated to determine
if a reduced light environment inhibits growth during winter months.
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CHAPTER X
VARIOUS WINTER TRAFFIC IMPACTS ON A „L93‟ CREEPING BENTGRASS
PUTTING GREEN
Introduction
In the transition zone, creeping bentgrass is desirable due to year-round green
color, ball roll, and overall playability. However, this turfgrass presents many challenges
throughout summer as well as winter seasons. During summer months, temperatures
exceeding 30oC result in shallow roots (Beard and Daniel, 1965), reduced carbohydrate
reserves (Huang and Gao, 2000), and increased disease susceptibility (Huang, 2001).
Management techniques to understand and possibly alleviate summer stress have been
documented (Guertal et al., 2005; Rodriguez et al., 2005; Bunnell et al., 2004).
Furthermore, winter temperature fluctuations within the transition zone present unique
challenges in bentgrass management. Superintendent daily dilemmas during winter
months in the transition zone include when to allow course set-up and play to initiate
when temperatures approach 0oC. Often, tee times are delayed or cancelled resulting in
lost revenues and tension between players and superintendents.
Water vapor condensation settling on turfgrass foliage becomes frost when
temperatures approach 0oC. Winter traffic, whether by foot, equipment, or animal,
during periods of frost typically cause damage, leaving turfgrass discolored. At colder
temperatures, processes such as photosynthesis and respiration are inhibited as cells enter
a gelatinous consistency resulting in possible membrane puncture (Fry and Huang, 2004).
177
Frost accumulation is also detrimental because ice crystals damage the protoplasm
(Beard, 1973). Plants maintaining an unsaturated fatty acid (double bond between carbon
atoms) composition enhances membrane fluidity (Cyril et al., 2002), thereby reducing
foliage damage.
Several management techniques are available to minimize winter injury. During
cool winter months at the Old Course in St. Andrews, golfers are required to use artificial
mats when hitting shots from fairways to minimize divot damage and subsequent slow
spring recovery (Hartwiger, 2005). Using insulated (straw or curled wood mat)
protective covers increase soil temperatures by 4.3oC and reduce seasonal soil
temperature variation, enhancing turfgrass winter survival (Dionne et al., 1999). Lightly
syringing greens prior to daily traffic and restricting golf cart access on fairways, tees,
and greens until temperatures exceed 0oC can also minimize winter-kill or damage
(White, 1984). Application of abscisic acid (ABA) has been shown to enhance freezing
tolerance (Gusta et al., 1996), while a proper fertility program can minimize winter injury
(Webster and Ebdon, 2005).
Numerous studies have been conducted to determine the diversity of turfgrass
freezing stress tolerance (Gusta et al., 1980; Rajashekar et al., 1983; Ebdon et al., 2002;)
and to determine turfgrass survival with or without snow and ice cover removal
(Tompkins et al., 2000; Tompkins et al., 2004; Valverde and Minner, 2007;). All of these
studies were performed in northern United States of America climates and to date,
research has not been reported attempting to quantify the effects of winter traffic injury
on bentgrass grown in the transition zone. Since light to heavy frost occurs on golf
178
courses in temperate climatic regions, superintendents must decide what time and type of
traffic are allowed on their golf courses, while minimizing turfgrass damage and meeting
player satisfaction. The main objective of this study was to access variable traffic
impacts to a creeping bentgrass putting green during winter months and determine
residual effects in spring and summer including 1) comparing 0700 and 0900 traffic
impacts to winter turfgrass quality; 2) comparing foot and walk behind mower traffic
impacts to turfgrass quality; and 3) investigating winter traffic residual effects on spring
and summer turfgrass performance.
Materials and Methods
This 2-year research project was conducted at Clemson University, Clemson, SC
from 1 December 2005 and 2006 to 1 August 2006 and 2007 on „L93‟ creeping bentgrass
field research plots established in 2002 with soil profile construction approximate to
USGA (United States Golf Association) recommendations (USGA, 1993). Although
simulated traffic treatments were terminated on 1 March 2006 and 2007, data collection
continued through spring and summer to evaluate any residual effects from winter traffic.
Treatments consisted of no traffic (control), foot traffic at 0700 (F7) and 0900 (F9), and
walk behind mower traffic (rolling) at 0700 (R7) and 0900 (R9). Traffic treatments were
applied at 0700 and 0900 when surface temperatures were below 0oC at 0700. Foot
traffic included ~75 steps within each plot using size 10 SP-4 Saddle Nike golf shoes
(soft-spiked sole) which ensured complete coverage of the plot. The majority of traffic
applications for each year were made by a person weighing 75 kg. A Toro®
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Greensmaster® 800 walk behind greens mower (Greenmaster® 800, The Toro Company,
Bloomington, MN) weighing 92 kg with a 46 cm roller was used to simulate rolling
traffic. One pass was made per plot. Plot dimensions were 46 cm in width by 120 cm in
length, similar width of the mower ensuring complete coverage of the plot. Therefore,
regardless of traffic type, the entire plot area was trafficked. Plots were always rolled and
not mowed when surface temperatures were below 0oC. Mowing occurred over the entire
plot area when surface temperatures were above 7.2oC on non-treatment days.
Depending on air temperature, the bentgrass green was mowed at 3.2 mm three
times weekly during winter months. In early January each year, a combination of 10N-
1.3P-4.2K and 5N-0P-5.8K liquid fertilizers (Progressive Turf, LLC., Ball Ground, GA)
was applied with nitrogen (N) at 4.9 kg ha-1
. Disease occurrence was minimal during the
study period, therefore, no fungicides were applied. Beginning in March and continuing
through August, mowing occurred six to seven times weekly at 3.2 mm. Nitrogen was
provided every 2-weeks at a rate of 9.7 kg ha-1
using Progressive Turf liquid fertilizers
from 15 March to 31 May 2006 and 2007. Following hollow tine aerification (1.3 cm
diam. tines 10 cm in length with 5.0 cm spacing) in spring 2006 and 2007, N was applied
at a rate of 24.4 kg ha-1
using 18N-1.3P-14.9K greens grade granular fertilizer
(Anderson‟s, Maumee, OH). Chlorothalonil (11.8 L ha-1
), Azoxystrobin (48.8 kg ha-1
),
and Mefonoxam (6.4 L ha-1
) were applied as needed to prevent dollar spot (Sclerotinia
homoeocarpa F.T. Bennet), pythium (Pythium spp.), and brown patch (Rhizoctonia
solani Kuhn.) occurrence, respectively.
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Data Collection
Collected data included surface and soil temperatures (7.6 cm depth) (model
#9840, Taylor, Oakbrook, IL), visual TQ, clipping yield, chlorophyll concentration, root
TNC, bulk density, and water infiltration rates. Surface (model #1455, Taylor,
Oakbrook, IL) and soil (7.6 cm depth) temperatures were recorded after each traffic
application (24 dates) during winter months at 0700, 0900, and solar noon.
Turfgrass quality ratings were recorded after each treatment application (24 rating
dates for both years) based on color, density, texture, and uniformity of the bentgrass
surface. Turfgrass quality scores were also recorded weekly and averaged per month
from March to August, 2006 and 2007. Quality was visually evaluated from 1 to 9, 1 =
brown, dead turfgrass, 6 = minimal acceptable turfgrass, 9 = ideal green, healthy
turfgrass.
Clipping yields (g m-2
) were collected following 8, 16, and 24 traffic applications,
mid-May, and mid-August for both years. Shoots were harvested with a Toro® walk
behind greens mower. For winter collection, the bentgrass green was not mowed for
three days to ensure adequate tissue sample due to slow shoot growth of bentgrass during
the winter. However, for spring and summer collection, the bentgrass green was not
mowed for one day prior to clipping yield collection. After collection, shoots were dried
in an 80oC oven for 48-hours to ensure complete tissue dehydration, then weighed
(McCullough et al., 2006).
Shoot chlorophyll (mg g-1
) was measured following 8, 16, and 24 traffic
applications, mid-May, and mid-August for both years. Fresh clippings were collected
181
from each plot using a Toro® walk behind greens mower following three days of growth
and immediately placed in a plastic bag inside a covered bucket to prevent sunlight
degradation. Clippings were weighed (0.1g) and placed in a glass test tube (1.0 cm in
width and 14.8 cm in length) with 10 mL of dimethyl sulfoxide (DSMO) (Hiscox and
Israelstam, 1979). Samples were incubated in 65 oC water on a hot plate (PC-600,
Corning, Corning, NY) for 1.5-hour and continuously shaken. Upon completion,
remaining extract (2 mL) was transferred into cuvettes. Absorbance values were
recorded at 663 nm and 645 nm wavelengths using a Spectrophotometer (GenesysTM
20,
ThermoSpectronic, Rochester, NY). Blanks were initially run and also after every sixth
sample as an internal control. The following formula was used to calculate total
chlorophyll (mg g-1
): (8.02 * D663 + 20.2 * D645) * 0.1 (Arnon, 1949).
Root tissues for TNC (mg g-1
) analysis was collected first week in May for both
years. Root tissue was harvested using a bulk density sampler which extracted 154.4 cm3
core samples (10.2 cm depth) prior to sunrise to minimize any diurnal fluctuations.
Following soil removal, root tissue samples were stored at -75oC until freeze dried at -
40oC for 2-weeks to cease all metabolic activity. Samples were then ground using an A-
10 plant grinder (IKA Works, Inc., Wilmington, NC). Grounded samples were
rehydrated with 100 L of 80% ethanol (EtOH) and 2 mL of 0.1 M sodium acetate buffer
(pH 4.5) in glass test tubes 13 X 100 mm. Rehydrated samples were placed in boiling
water for 1-hour, cooled for 1-hour and repeated. Then, 2 mL of invertase (Sigma I-
4753, 433 units mg-1
) and amyloglucosidase (Sigma A-7255, 23,000 units g-1
) were
added to solution. Samples were placed in a water bath (40 – 45oC) for three days and
182
vortexed three times daily. TNC analysis was performed using Nelson (1944) and
Somogyi (1952) procedures. 25 L of aliquot was removed and two reagents (copper
and arseno-molybdate) were added to the solution. Absorbance values were measured at
520 nm using a spectrophotometer.
Soil bulk density (10.2 cm depth) was collected end of February for both years
following 24 traffic applications by extracting 154.4 cm3 soil cores. Cores were oven
dried at 105oC for 10 days to ensure complete water evaporation. The following formula
was used to calculate bulk density: dry weight of sample (g) / volume of sample (cm3).
Water infiltration analysis (Bunnell et al., 2001) was performed end of February
in both years following 24 traffic applications using a double ring infiltrometer (model
13a, Turf-Tec International, Oakland Park, Fla.). One sample was taken per plot. The
outer ring had a diameter of 30.5 cm and the inner ring, 15.2 cm. The infiltrometer was
inserted into the turfgrass canopy at a depth of 2.5 cm. Rings were then filled to the top
of the infiltrometer with 10.2 cm of water. After water vacated the center ring,
infiltration rates were recorded based on how long the water took to absorb fully into the
soil.
Data Analysis
Treatments were arranged in a randomized complete block design with six
replications. In year II, plots were re-randomized within the identical plot dimensions of
year I because no residual effects were noted during spring and summer months in year I.
All statistical computations were conducted using analysis of variance (ANOVA) within
the Statistical Analysis System (version 9.1, SAS Institute, Cary, NC). Means were
183
separated by Fisher‟s Least Significant Difference (LSD) test with an alpha of 0.05.
Year*treatment interaction occurred for winter TQ scores, however, differences were
scale changes with similar trends, therefore, pooled data from year I and II are presented.
Results
Coldest monthly surface temperatures were noted in January. For all months,
surface temperatures at 0700 were ~11.2oC colder than 0900, while surface temperatures
at 0900 were ~9.8oC colder than solar noon. However, no differences were detected for
soil temperatures between 0700 and 0900, but solar noon soil temperatures were ~3.1oC
higher than at 0700 and 0900 across all months (Table A.2). Daily maximum
temperatures for year 1 and 2 were similar with few exceptions (Figure A.1). Compared
to historical data, year I was 2.9oC below, while year II was 4.2
oC above the average
maximum temperature in December. In January and February, both years were ~4.6oC
above and ~3.5oC below historical average maximum temperature, respectively. Based
on historical minimum average temperatures, both winters were ~5.7oC warmer (Figure
A.2). Compared to year 1, year 2 had 4.7oC warmer minimum temperatures from
December to mid-January, while temperatures were similar from end of January through
February each year.
All traffic treatments TQ was below the acceptable threshold of 6 by third traffic
application, while control TQ was 7.6 (Table 10.1). By the sixth traffic application, R7
TQ was 5.3, while control, F7, F9, and R9 remained above 6. However, F9 (7.1) had a
greater TQ score than R9 (6.4), while control had the greatest TQ (7.7) score. After nine
184
Table 10.1. Turfgrass quality of ‘L93’ creeping bentgrass without (control) and with
24 foot and rolling winter traffic applications at 0700 or 0900 recorded after each 24
traffic application dates from 1 December 2005 and 2006 to 1 March 2006 and 2007.
Traffic Day 3 Day 6 Day 9 Day 12 Day 15 Day 18 Day 21 Day 24
--------------------------------Turfgrass quality (1-9)†-------------------------------
Control‡ 7.6 7.7 7.3 7.5 7.1 7.5 7.0 7.1
F7 6.6 6.9 6.3 6.0 5.4 5.1 5.0 4.8
F9 6.8 7.1 6.9 6.5 6.4 6.5 6.3 5.9
R7 5.7 5.3 5.3 5.2 4.3 4.1 3.8 3.7
R9 6.8 6.4 6.3 6.4 6.2 5.6 5.8 5.4
LSD 0.44§
0.53 0.54 0.51 0.46 0.50 0.51 0.48 †Turfgrass quality based on a scale of 1 - 9, 1 = brown/dead turfgrass, 6 = minimally
acceptable turfgrass, 9 = ideal green, healthy turfgrass. ‡Abbreviations: Control = No traffic, F7 = Foot traffic at 0700, F9 = Foot traffic at 0900,
R7 = Rolling traffic at 0700, R9 = Rolling traffic at 0900, LSD = least significant
difference. Foot traffic consisted of ~75 steps using SP-4 Saddle Nike golf shoes (soft-
spiked sole). Rolling traffic was accomplished using a Toro® Greensmaster® 800 walk
behind mower. §Values within a column followed by the same letter are not significantly different at
P≤0.05 by protected LSD.
LSD = Least significant difference.
traffic applications, the R7 treatment had a 5.3 TQ score, while F7 had a TQ score of 6.3.
Also, R9 TQ was 6.3, while F9 TQ was 6.9. Similar trends continued from day 12
through day 24 ratings as R7 reduced TQ by ~1.0 units compared to F7 TQ. Visual TQ
for R9 on two rating dates (day 18 and 24) showed a 0.9 and 0.5 unit decline compared to
F9 TQ. On the last traffic application date, R7 had TQ of 3.7, while F7‟s TQ was 4.8.
On all rating dates, R7 showed a ~1.4 unit TQ decrease than R9, while F7 reduced TQ by
~1.1 units compared to F9 on most rating dates. Except R7 (5.8), all other treatments
185
Table 10.2. Turfgrass quality of ‘L93’ creeping bentgrass without (control)
and with 24 foot and rolling winter traffic applications at 0700 or 0900
recorded weekly and averaged per month from March to August, 2006 and
2007.
Traffic March April May June July August
----------------------------Turfgrass Quality (1-9)†-----------------------
Control‡ 7.1 7.8 7.9 7.6 7.5 6.6
F7 6.2 7.3 7.8 7.6 7.5 6.4
F9 6.5 7.3 7.7 7.3 7.6 6.3
R7 5.8 7.0 7.7 7.3 7.6 6.4
R9 6.5 7.3 7.7 7.4 7.4 6.6
LSD 0.30§ 0.33 NS NS NS NS
†Turfgrass quality based on a scale of 1 - 9, 1 = brown/dead turfgrass, 6 =
minimally acceptable turfgrass, 9 = ideal green, healthy turfgrass. ‡Abbreviations: Control = No traffic, F7 = Foot traffic at 0700, F9 = Foot traffic at
0900, R7 = Rolling traffic at 0700, R9 = Rolling traffic at 0900, LSD = least
significant difference, NS = not significant. Foot traffic consisted of ~75 steps
using SP-4 Saddle Nike golf shoes (soft-spiked sole). Rolling traffic was
accomplished using a Toro® Greensmaster® 800 walk behind mower. §Values within a column followed by the same letter are not significantly different
at P≤0.05 by protected LSD.
LSD = Least significant difference, NS = not significant.
reached acceptable TQ by March (Table 10.2). By April, all treatments were above the
acceptable TQ threshold of 6 indicating bentgrass had visually recovered from any winter
traffic damage. No TQ differences were noted from May to August ratings, however, TQ
scores began to decline for all treatments in August due to the onset of summer stress not
influenced by this winter study.
Winter traffic significantly impacted clipping yield (Table 10.3). In December,
compared to the control, F7 and F9 reduced clipping yield ~6.5%, while R7 and R9
reduced clipping yield ~24%, respectively. Similar trends continued in January and
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Table 10.3. Clipping yield (g m-2
) of ‘L93’ creeping bentgrass without
(control) and with 24 foot and rolling winter traffic applications at 0700 or
0900 in winter, spring, and summer months in year I and II.
Traffic December January February May August
------------------------------Clipping yield (g m-2
)-------------------------
Control† 1.74 1.55 1.27 1.31 1.27
F7 1.71 1.27 1.21 1.27 1.28
F9 1.57 1.38 1.16 1.23 1.24
R7 1.50 1.10 1.04 1.32 1.42
R9 1.32 1.04 0.95 1.26 1.32
LSD 0.17‡ 0.23 0.22 NS NS
†Abbreviations: Control = No traffic, F7 = Foot traffic at 0700, F9 = Foot traffic at
0900, R7 = Rolling traffic at 0700, R9 = Rolling traffic at 0900, LSD = least
significant difference, NS = not significant. Foot traffic consisted of ~75 steps
using SP-4 Saddle Nike golf shoes (soft-spiked sole). Rolling traffic was
accomplished using a Toro® Greensmaster® 800 walk behind mower. ‡Values within a column followed by the same letter are not significantly different
at P≤0.05 by protected LSD.
LSD = Least significant difference, NS = not significant.
February indicating rolling traffic negatively impacted shoot growth greater than foot
traffic. In February, no differences were noted between foot traffic and the control, while
R7 and R9 reduced clipping yield ~28% compared to the control. No residual effects
from winter traffic on shoot growth were noted in May or August.
Shoot chlorophyll concentration was not impacted in December or January, but
the control had ~18% higher chlorophyll concentration compared to F7 in February
(Table 10.4). In May and August, no differences were noted for chlorophyll
concentration indicating no winter traffic residual effects. After 24 traffic applications
(foot or rolling) at 0700 or 0900, no impact was noted on bulk density or water
infiltration rates (Table 10.5). Also, root TNC in May was unaffected by any winter
traffic treatments (Table 10.5).
187
Table 10.4. Chlorophyll (mg g-1
) concentration of ‘L93’ creeping bentgrass
without (control) and with 24 foot and rolling winter traffic applications at
0700 or 0900 recorded in winter, spring, and summer months in year I and
II.
Traffic December January February May August
-------------------------------Chlorophyll (mg g-1
)------------------------
Control† 1.91 1.60 1.34 2.68 2.66
F7 2.07 1.54 1.14 2.77 2.66
F9 1.97 1.58 1.21 2.59 2.70
R7 2.01 1.53 1.23 2.58 2.78
R9 2.04 1.53 1.21 2.72 2.67
LSD NS NS 0.13‡ NS NS
†Abbreviations: Control = No traffic, F7 = Foot traffic at 0700, F9 = Foot traffic
at 0900, R7 = Rolling traffic at 0700, R9 = Rolling traffic at 0900, LSD = least
significant difference, NS = not significant. Foot traffic consisted of ~75 steps
using SP-4 Saddle Nike golf shoes (soft-spiked sole). Rolling traffic was
accomplished using a Toro® Greensmaster® 800 walk behind mower. ‡Values within a column followed by the same letter are not significantly
different at P≤0.05 by protected LSD.
LSD = Least significant difference, NS = not significant.
Table 10.5. Soil bulk density (g cm-3
) and infiltration rates (cm h-1
) collected
end of February and root total non-structural carbohydrates (TNC) (mg g-1
)
collected in May following 24 treatment application dates with and without
(control) foot and rolling traffic at 0700 or 0900 from 1 December 2005 and
2006 to 1 March 2006 and 2007.
Traffic Bulk Density Infiltration Root TNC
Control† 1.72 4.20 47.37
F7 1.71 4.80 43.72
F9 1.72 5.34 48.69
R7 1.71 4.30 46.62
R9 1.70 4.58 40.03
LSD NS NS NS †Abbreviations: Control = No traffic, F7 = Foot traffic at 0700, F9 = Foot traffic at
0900, R7 = Rolling traffic at 0700, R9 = Rolling traffic at 0900, LSD = least
significant difference, NS = not significant. Foot traffic consisted of ~75 steps
using SP-4 Saddle Nike golf shoes (soft-spiked sole). Rolling traffic was
accomplished using a Toro Greensmaster 800 walk behind mower.
LSD = Least significant difference, NS = not significant.
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Discussion
When temperatures are at or near freezing, decisions about when to allow normal
golf course management operations, such as course set-up, are generally experience-
based. Previous research was lacking on winter traffic damage to bentgrass greens and
subsequent performance in the spring and summer in the southern transition zone where
golf play continues through winter months. Based on these results, time and type of
traffic negatively impacted bentgrass winter performance and playability. By day 24, R7
and R9 decreased TQ by 1.1 and 0.5 units compared to F7 and F9, respectively. Also, F7
and R7 decreased TQ by 1.1 and 1.7 units compared to F9 and R9, respectively. This can
be attributed to more complete frost dissipation as frost melt had occurred by 0900 on
cloudless mornings. Surface temperatures on simulated traffic days were consistently
below 0oC at 0700, while surface temperatures at 0900 were >6.8
oC. Regardless of
traffic type, all treatments were deemed unacceptable following 24 traffic treatments on
the coldest days from December to February. However, F9 TQ was at or near the
acceptable threshold throughout the winter months. Averaged across all TQ rating dates,
R7 decreased TQ by ~1.1 units compared to F7. Rolling traffic had more surface
discoloration than foot traffic due to heavier impacts of the mower. The contact area of
the roller was ~115 cm2 (46 cm roller width with 2.5 cm of the roller consistently
contacting the turfgrass surface) with a pressure of 0.80 kg cm-2
, while one foot traffic
pressure was 0.31 kg cm-2
with a contact area of 240 cm2. Therefore, the walk behind
mower applied nearly three times the pressure of foot traffic. Carrow and Petrovic
(1992) also noted added weight increased wear injury.
189
Rolling traffic reduced bentgrass shoot growth ~28% compared to control,
however, no differences in chlorophyll, bulk density, or water infiltration were detected
between treatments in February. Since bulk density was unaffected following 24 winter
traffic applications, the primary stress in this study was wear and not soil compaction as
reported by Carrow and Petrovic, 1992. Traffic stress on Kentucky bluegrass (Poa
Pratensis L.) also reduced shoot growth (Ervin and Koski, 2001). Shoot growth
suppression can be attributed to weight being applied to the bentgrass surface with
possible physical damages to shoot tissues. Further studies are needed to specifically
examine winter traffic damages to above ground tissues. Spring and summer TQ, root
TNC, and shoot chlorophyll data indicate winter traffic damage is limited to winter and
early spring months. By mid- to late-spring and throughout summer, all plots fully
recovered.
Results obtained in this study may vary on other field sites due to variable micro-
environments on golf courses, in particular, shade. While not examined in this study,
shaded areas may be more difficult for winter management because surface frost
dissipation is slower than greens receiving full early morning sunlight. Also, slopes
facing north or northeast receive less direct sunlight during winter morning hours and are
more prone to winter injury due to prolonged frost periods (McCarty et al., 2005).
Winter shade, in combination with winter traffic, is potentially damaging due to shorter
daylengths, reduced light intensities, and solar elevation angles. These factors can
enhance frost accumulation and prolong frost coverage.
190
Conclusion
Turfgrass managers should carefully consider whether to allow traffic on turfgrass
surfaces when frost is present. Traffic weight appears to be the contributing factor for
increased surface discoloration was weight of traffic. Although, foot traffic was less
damaging than equipment traffic, some surface discoloration was noted. Even at 0900
when temperatures were above freezing and frost had dissipated, bentgrass injury was
observed. However, by late spring and summer, TQ differences were no longer detected.
Therefore, if winter injury occurs on a bentgrass green in the eastern part of the transition
zone, full recovery should be expected.
Future studies could investigate winter traffic impacts at later time periods (i.e.,
0730, 0800, 0830, 0900, or 0930) and temperature ranges (i.e., -1-2
oC, 2-4
oC, or 5-7
oC) to
monitor the traffic impacts. This type of study would provide turfgrass managers with
information that would help them manage play and maintenance while minimizing injury
to bentgrass putting greens during winter months. In addition, creeping bentgrass
cultivars may perform differently in response to winter traffic due to different root zone
mixtures, fertility regimes (i.e., nitrogen, calcium, and potassium), and equipment type.
These types of studies could also be conducted on warm-season turfgrass putting greens
either overseeded or painted in areas where multiple light to medium frosts occur during
winter months. Finally, the impacts of lightly syringing greens to dissipate frost
accumulation and reduce traffic damage warrants investigations.
191
CHAPTER XI
SUMMARY AND PERSPECTIVES
Primary objectives of this dissertation were to determine the genetic diversity of
bermudagrasses grown in full-sunlight and shade, impacts of shade and winter cultural
practices on bermudagrass spring transition, management recommendations to enhance
bermudagrass putting greens under shade, and the impact different types of light on
warm-season turfgrasses. Secondary objectives of this dissertation were to determine
winter shade and traffic impacts on creeping bentgrass putting greens.
A field study determined the morphological and physiological characteristics of
42 bermudagrass cultivars selected from the 2002 National Turfgrass Evaluation Program
(NTEP) in spring, summer, and fall. Experimental bermudagrass cultivars from breeding
programs were comparable, and at times, out-performed industry standards based on
parameters measured in the spring, summer, and fall. In a greenhouse study, the same 42
bermudagrass cultivars were subjected to 64% continuous artificial shade for 60 days.
Cultivars with best shade-tolerance were Celebration, TiftNo.4, TiftNo.1, and
Transcontinental, while most shade-sensitive cultivars included SWI-1014, Arizona
Common, Sundevil, SR 9554, GN-1, and Patriot. Both of these studies demonstrate
genetic variability exists within bermudagrass and future improvement of breeding
improved bermudagrass cultivars should be expected.
In two lysimeter projects, fairway and ultradwarf bermudagrasses were subjected
to shade in late-winter and continued shade stress through spring and summer months.
192
Also, for the ultradwarf bermudagrass, various winter cultural practices were investigated
to determine best winter management practices. For fairway type grasses, Celebration
and TiftNo.4 did not show significant SGU delays due to shade in year II, however,
Yukon and Riviera delayed SGU 11% and 50% compared to full-sunlight treatments on 9
May 2007. Celebration and TiftNo.4 showed a ~1.3 and ~1.7 unit TQ increase compared
to other cultivars in July when grown in shade, however, all cultivars TQ was below the
acceptable threshold of 7 by 31 July. In another lysimeter study, regardless of winter
cultural practice, shade reduced TifEagle bermudagrass SGU and summer TQ ratings
compared to full-sunlight treatment. However, colorant use enhanced SGU ratings
compared to overseed and dormant treatments under full-sunlight and shade. This study
indicates colorant-use may provide an alternative to overseeding for bermudagrass by
providing adequate winter color at certain sites and a stronger bermudagrass base
compared to overseeding.
A two-year field study determined best management practices to enhance a
Champion bermudagrass putting green under shade. Treatments included 55% full-day
shade, TE applications (0.05 kg a.i. ha-1
2wk-1
), iron (Fe) applications (2.7 kg a.i. ha-1
2wk-1
), and N applications as urea (46-0-0) at rates of 147, 293, and 437 kg ha-1
yr-1
.
Results indicate reducing N rates linearly increased TQ scores under 55% full-day shade.
Also, applying TE resulted in a linear TQ increase for full-sunlight and shade-grown
Champion bermudagrass. Iron applications had minimal impacts on parameters
measured. In conclusion, while adjusting chemical and cultural management practices
193
reduced shade stress symptoms, 55% full-day shade for three months resulted in
unacceptable quality, regardless of management practices.
In the greenhouse, two repeated studies were conducted to understand the
physiological and morphological responses of Diamond zoysiagrass, Sea Isle 2000
seashore paspalum, Tifway bermudagrass, and Celebration bermudagrass to various light
spectral qualities. Light treatments included a full-sunlight control and four different
color shade cloths filtering wavelengths 560 - 720 nm (blue shade cloth), 360 – 520 nm
(yellow shade cloth), 360 - 560 nm (red shade cloth) and 360-720nm (black shade cloth).
Percent light reduction for each cloth was ~65%. Overall, black shade most negatively
inhibited parameters measured followed by blue shade, while yellow and red shade
performed similarly. For turfgrasses, Diamond was the most shade-tolerant, while
Tifway was the most shade-sensitive. Celebration and Sea Isle 2000 performed similarly.
This study implies different types of shade significantly impact the performance of warm-
season turfgrasses.
A winter field study was conducted to evaluate winter shade tolerance of „L93‟
creeping bentgrass under various reduced light environments (55% and 95%), including
effects of morning vs. afternoon shade, effect of trinexapac-ethyl (TE) (4-(cyclopropyl- -
hydroxy-methylene)-3,5-dioxy-cyclohexanecarboxylic acid ethyl ester) application on
shade tolerance, and summer month performance following a winter shade environment.
Under shade stress, applying TE every two weeks during winter negatively impacted
bentgrass growth and color, while morning or afternoon shade minimally impacted
parameters measured. Based on this study, moderate to heavy winter shade may not limit
194
creeping bentgrass performance as a putting green in the transition zone. In a winter
traffic field study, treatments consisted of no traffic (control), foot traffic, and walk
behind mower traffic (rolling) at 0700 and 0900 when canopy temperatures were at or
below 0oC. The 0700 rolling traffic treatment decreased TQ by ~1.1 units compared to
foot traffic at 0700. However, by the end of March, all treatments had acceptable TQ.
This study indicates bentgrass damage due to winter traffic is limited to winter and early
spring months and full recovery should be expected by summer.
Shade is a unique stress. In a natural environment, shade is dynamic and ever-
changing making it very difficult to capture this unique environment through traditional
field and greenhouse studies. Due to this, conducting shade research is difficult and
perhaps an explanation why bermudagrass shade stress research is minimal. Although
this dissertation has addressed many gaps in the literature, many questions remain
regarding bermudagrass and shade.
This dissertation has shown that fairway type bermudagrasses vary in response to
shade stress. Future studies to establish why these bermudagrass cultivars are relatively
shade-tolerant include determining photosynthetic rates, characterizing GA levels (i.e.,
GA1, GA12, or GA53 via mass spectroscopy), exploring anatomical development, and
investigating the importance of sunflecks and its contribution to photosynthesis. While
fairway type bermudagrasses are diverse in response to shade, ultradwarf bermudagrass
shade research is minimal. Although ultradwarf bermudagrasses are gaining popularity,
relative shade-tolerance of many of these cultivars remains unknown.
195
The majority of shade research focusing on light quality has been greenhouse
studies, therefore, field evaluations are warranted to confirm results obtained from an
artificial greenhouse environment. Also, comparing the response of turfgrass species
and/or cultivars to altered R:FR ratios is lacking. This dissertation has indicated different
light spectrums impact warm-season turfgrasses differently. However, the same type of
light was filtered all day, which is a limitation of this study. A future field study of
interest would be to compare how alternating between different types of spectral shade in
the morning or afternoon effect turfgrass performance.
While this dissertation and previous research have proven N reductions is
beneficial for turfgrass shade performance, many question still remain regarding fertility
regimes when shade is problematic. For example, while reducing N is prudent, numerous
N forms and sources exist in the market. Future studies addressing how N form (liquid,
granular, combination of both forms) and N type (calcium nitrate, ammonium sulfate,
urea, and ammonium nitrate) effect turfgrass growth and development under shade is
warranted. Also, investigating other macro and micronutrient rates for shade-tolerance
improvement is needed. Another nutrient of interest is silicon (Si). In other plant
disciplines, Si has improved salt stress in rice (Matoh et al., 1986), barley (Liang et al.,
1996), cucumber (Zhu et al., 2004), tomato (Romero-Aranda et al., 2006), and wheat
(Ahmad et al., 1992) and aluminum stress in Zea Mays (Barcelo et al., 1993; Corrales et
al., 1997). Silicon has also been proven to enhance drought tolerance and photosynthetic
capacity in bentgrass (Schmidt et al., 1999). Future studies determining the importance
of Si as a stress reducing nutrient in turfgrass is needed.
196
Plant growth regulator applications have become a routine component of turfgrass
management. This dissertation and previous research has firmly established TE improves
warm- and cool-season turfgrasses response to shade when temperatures are optimal for
growth. However, questions still remain about PGR applications under shade stress.
Future studies investigating various TE rates, intervals of TE applications, tank mixing
TE with other PGRs, and comparing TE to other GA inhibiting PGRs to further improve
the response of turfgrasses under shade stress are needed. Perhaps the most significant
aspect ignored in this dissertation and previous bermudagrass shade research is traffic
effects when TE is used. Adding a traffic stress component when applying TE under
shade stress would be a practical research area to pursue with great benefit to the
industry.
Another interesting area to pursue in shade research is to study the impact of tree
roots and air restriction on the performance of turfgrasses. Only two studies found have
focused on tree root competition with turfgrasses (Whitcomb, 1972; Whitcomb and
Roberts, 1973). However, difficulty in quantifying exactly how much water and nutrients
a tree root system out-competes a turfgrass root system is a limiting factor for this type of
future research. Previous research has established that air restriction is a stress
independent of shade, however, the few studies that exist have been limited to only a few
turfgrass cultivars. Future studies of interest would be to determine turfgrass species
and/or cultivar genetic variation to wind restriction stress.
Finally, utilizing bio-technology may be a future avenue in improving responses
of turfgrasses to shade stress. At Ohio State University, Yan (2007) overexpressed GA 2-
197
oxidase genes responsible for gibberellic acid production, overexpressed PHYB genes
from Arabidopsis causing dwarfing characteristics, and overexpressed BAS1 gene
regulating brassinosteroid levels causing dwarf-type growth. For all genes
overexpressed, results indicated improved shade tolerance in creeping bentgrass.
Continuing to explore the potential of transgenic approaches and determine the feasibility
of this technology to enhance shade tolerance of existing turfgrass species would be
beneficial.
198
APPENDICES
199
Appendix A
Additional Tables and Figures
Table A.1. Bermudagrass (Cynodon dactylon (L.) Pers.) cultivars selected for a field and greenhouse
study to evaluate morphological and physiological characteristics and shade-tolerance at the
Clemson University field research plots and greenhouse research complex.
Cultivar Type Sponsor Address
„Sunstar‟ Seeded Lesco, Inc. 1301 East 9th St., Suite 1300, Cleveland, OH 44114
„B-14‟ Seeded Lesco, Inc. 1301 East 9th St., Suite 1300, Cleveland, OH 44114
„SWI-1003' Seeded Seeds West, Inc. 508 East 16th Street, Yuma, AZ 85365
„SWI-1012‟ Seeded Seeds West, Inc. 508 East 16th Street, Yuma, AZ 85365
„'SWI-1014‟ Seeded Seeds West, Inc. 508 East 16th Street, Yuma, AZ 85365
„SWI-1041‟ Seeded Seeds West, Inc. 508 East 16th Street, Yuma, AZ 85365
„SWI-1044‟ Seeded Seeds West, Inc. 508 East 16th Street, Yuma, AZ 85365
„SWI-1045‟ Seeded Seeds West, Inc. 508 East 16th Street, Yuma, AZ 85365
„SWI-1046‟ Seeded Seeds West, Inc. 508 East 16th Street, Yuma, AZ 85365
„Arizona
Common‟ Seeded Standard Entry ------------------------------------------
„NuMex Sahara‟ Seeded Standard Entry ------------------------------------------
„Princess 77‟ Seeded Standard Entry ------------------------------------------
„Mohawk‟ Seeded Seeds West, Inc. 508 East 16th Street, Yuma, AZ 85365
„FMC-6‟ Seeded Seeds West, Inc. 508 East 16th Street, Yuma, AZ 85365
„SWI-1001 Seeded Seeds West, Inc. 508 East 16th Street, Yuma, AZ 85365
„Tift No.3‟ Vegetat-
ive
Wayne Hanna -- USDA-
ARS P.O. Box 748, Tifton, GA 31793
„Tift No.4‟ Vegetat-
ive
Wayne Hanna -- USDA-
ARS P.O. Box 748, Tifton, GA 31793
„Tifway‟ Vegetat-
ive Standard Entry ------------------------------------------
„Midlawn‟ Vegetat-
ive Mississippi State University P.O. Box 9555, Mississippi State, MS 39762
„Tifsport‟ Vegetat-
ive Standard Entry ------------------------------------------
„Sundevil‟ Seeded Jacklin Seed/Simplot 5300 W. Riverbend Ave., Post Falls, ID 83854
„Southern Star‟ Seeded Jacklin Seed/Simplot 5300 W. Riverbend Ave., Post Falls, ID 83854
„MS-Choice‟ Vegetat-
ive Mississippi State University P.O. Box 9555, Mississippi State, MS 39762
„Transcontinental‟ Seeded Turf-Seed, Inc. 7644 Keene Rd. NE, Gervais, OR 97026
„CIS-CD5‟ Seeded DLF International Seeds 175 W. H St., P.O. Box 229, Halsey, OR 97348
„CIS-CD6‟ Seeded DLF International Seeds 175 W. H St., P.O. Box 229, Halsey, OR 97348
„CIS-CD7‟ Seeded DLF International Seeds 175 W. H St., P.O. Box 229, Halsey, OR 97348
„Panama‟ Seeded Barenbrug USA 33477 HWY 99E, P.O. Box 239, Tangent, OR 97389
„La Paloma‟ Seeded Seed Research of OR, Inc. 27630 Llewellyn Rd., Corvallis, OR 97330
200
Table A.1. Bermudagrass (Cynodon dactylon (L.) Pers.) cultivars selected for a field and greenhouse
study to evaluate morphological and physiological characteristics and shade-tolerance at the
Clemson University field research plots and greenhouse research complex (continued).
„SR 9554‟ Seeded Seed Research of OR, Inc. 27630 Llewellyn Rd., Corvallis, OR 97330
„Yukon‟ Seeded Seed Research of OR, Inc. 27630 Llewellyn Rd., Corvallis, OR 97330
„Aussie Green‟ Vegetat-
ive Greg Norman Turf Co. 4366 E. Kinsey Rd, Avon Park, FL 33825
„GN-1‟ Vegetat-
ive Greg Norman Turf Co. 4366 E. Kinsey Rd, Avon Park, FL 33825
„Premier‟ Vegetat-
ive Trinity Turf Nursery 17199 Zipper Rd., Pilot Point, TX 76258
„Ashmore‟ Vegetat-
ive Blue Moon Farms, LLC 811 Mountain River Rd., Lebanon, OR 87355
„Patriot‟ Vegetat-
ive Oklahoma State University 136 Ag Hall, Stillwater, OK 74078
„OKC 70-18‟ Vegetat-
ive Oklahoma State University 136 Ag Hall, Stillwater, OK 74078
„Celebration‟ Vegetat-
ive Sod Solutions P.O. Box 460, Mt. Pleasant, SC 29465
„TiftNo.1‟ Seeded
Wayne Hanna -- USDA-
ARS P.O. Box 748, Tifton, GA 31793
„TiftNo.2‟ Seeded
Wayne Hanna -- USDA-
ARS P.O. Box 748, Tifton, GA 31793
„Sunbird‟ Seeded Turf-Seed, Inc. 7644 Keene Rd. NE, Gervais, OR 97026
201
Table A.2. Average monthly surface and soil (7.6 cm depth) temperatures (oC)
of ‘L93’ creeping bentgrass during each 24 traffic treatment applications at
0700, 0900, and solar noon from 1 December, 2005 and 2006 to 1 March 2006
and 2007.
Surface temperatures (oC) Soil temperatures (
oC)
Time December January February December January February
0700 -4.0 -3.1 -3.5 3.3 3.5 2.6
0900 8.3 6.8 7.8 3.1 3.8 2.6
Solar
Noon 20.0 17.0 15.2 6.0 6.7 6.1
LSD 2.5† 2.5 2.6 1.3 1.7 1.5
†Values within a column followed by the same letter are not significantly different at
P≤0.05 by protected LSD.
LSD = least significant difference.
Figure A.1. Daily and historical average maximum temperatures at Clemson University,
Clemson, SC in year I and II from 1 December to 28 February 2005 – 2007.
0
5
10
15
20
25
30
Year 1
Year 2
Average
1 December to 28 February 2005 - 2007
oC
202
Figure A.2. Daily and historical average minimum temperatures at Clemson University,
Clemson, SC in year I and II from 1 December to 28 February 2005 – 2007.
-10
-5
0
5
10
15
Year 1
Year 2
Average
1 December to 28 February 2005 - 2007
oC
oC
203
Appendix B
Chlorophyll Extraction with DMSO
1. Weigh 0.1 g fresh shoot tissue into Erlenmyer flasks.
2. Add 10 mL of Dimethyl Sulfoxide to each flask. Cover with rubber stopper.
3. Incubate in 65 C water shake bath for 1.5 h.
4. Transfer extract into spectrophotometer using pipetter.
5. Measure and record absorbance values at 663 nm and 645 nm wavelengths.
6. Chlorophyll content is determined by the following formula (Arnon, 1949).
(20.2 * D645 + 8.02 * D663) * 0.1 = mg chlorophyll g-1
fresh tissue
D663 and 645 = absorbance values at given wavelengths
204
Appendix C
Procedure for Nelson‟s Assay for TNC Analysis
Aliquot preparation
1. Weigh 50 mg dry tissue sample in 13 x 100 mm test tube.
2. Add 100 µl of 80% ethanol.
3. Add 2 ml of 0.1 M sodium acetate buffer.
4. Place test tubes in boiling water for 1 h; allow cooling for 1 h, and repeat. Allow
solution to cool before adding enzymes.
5. Add 1.0 ml of each enzyme solution. Keep enzyme solutions on ice.
a. Invertase (Sigma I-4753, 433 units mg-1
)
- 5 units / ml in 0.1 M acetate buffer
b. Amyloglucosidase (Sigma A-7255, 23,000 units g-1
)
- 50 units / ml in 0.1 M acetate buffer
6. Incubate for 3 days at 40-45 C and vortex 3 times day-1
.
7. Allow to settle until clear.
8. Remove 25 µl of aliquot for TNC analysis.
205
Buffers, Reagents, and Standard Glucose Curves
Sodium Acetate Buffer
1. For 2000 ml of 0.1 M buffer, weigh 5.56 g of sodium acetate.
2. Dissolve in approximately 1600 ml deionized water.
3. Adjust pH to 4.5 using 1 N acetic acid.
4. Bring to 2000 ml volume.
5. Store at 3 C.
Copper Reagent
1. Dissolve 28 g of anhydrous sodium phosphate dibasic (Na2HPO4) and 4 g K-Na-
tartate (Rochelle salt) in approximately 650 ml of deionized water.
2. Add 100 ml of 1 N NaOH (4g NaOH 100 ml-1
H2O) while stirring.
3. Add 80 ml of 10% copper sulfate (8g CuSO4 80 ml-1
H2O)
4. Add 180 g of anhydrous Na2SO4.
5. Bring to 1000 ml volume and mix well.
6. Allow to settle at room temperature for 24 h.
7. Decant and save clear supernatant.
8. Store in brown bottle at room temperature.
Arseno-Molybdate (ASMO) Reagent
1. Dissolve 25 g of ammonium molybdate (NH4MoO4) in approximately 400 ml.
206
2. Add 21 ml of concentrated sulfuric acid.
3. Add 3 g of sodium arsenate (Na2HAsO4•7H2O) dissolved in 25 ml of deionized water.
4. Bring to 500 ml and mix well.
5. Incubate at 37 C for 24-48 h.
6. Store in brown bottle at room temperature.
Glucose Standards
Glucose Concentration glucose (g l-1
) Dilution for 10 ml of Standard
0.8 µmol 100 μl-1
(stock) 1.4408 g l-1
10.00 ml stock : 0.00 ml water
0.7 µmol 100 μl-1
(stock) 1.2607 g l-1
8.75 ml stock : 1.25 ml water
0.6 µmol 100 μl-1
(stock) 1.0806 g l-1
7.50 ml stock : 2.50 ml water
0.5 µmol 100 μl-1
(stock) 0.9005 g l-1
6.25 ml stock : 3.75 ml water
0.4 µmol 100 μl-1
(stock) 0.7204 g l-1
5.00 ml stock : 5.00 ml water
0.3 µmol 100 μl-1
(stock) 0.5403 g l-1
3.75 ml stock : 6.25 ml water
0.2 µmol 100 μl-1
(stock) 0.3602 g l-1
2.50 ml stock : 7.50 ml water
0.1 µmol 100 μl-1
(stock) 0.1801 g l-1
1.25 ml stock : 8.75 ml water
0.0 µmol 100 μl-1
(stock) 0.0000 g l-1
0.00 ml stock : 10.00 ml water
TNC Calculation
1. Pipette 25 µl of aliquot (samples and glucose standards) into 13 x 100 mm test tubes.
2. Add 1.0 ml of copper reagent, mix, and place in boiling water bath for 20 minutes.
3. Remove samples and allow cooling for 5 minutes in room temperature water bath.
207
4. Add 0.5 ml of ASMO, mix well with vortex, and pipette into cuvettes.
5. Read absorbance at 520 nm.
6. Calculate linear regression of glucose standard curve.
7. Solve for glucose concentration using linear regression equation and absorbance
value.
Figure C.1. Standard curve used in Nelson‟s assay for determining total nonstructural
carbohydrate content in bermudagrass and bentgrass shoots and roots.
y = 0.8805x - 0.0288
R2 = 0.9704
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0 0.2 0.4 0.6 0.8 1
Glucose standard (μg glucose 100 μL-1
)
Ab
sorb
an
ce (
52
0 n
m)
208
Appendix D
Illustrations
Illustration D.1. TiftNo.5 bermudagrass anatomical features including bundle sheath (a),
mesophyll cells (b), vascular bundle (c), and epidermal cells (d). Image recorded on 20
December 2005 at the Clemson University Research Park, Clemson, SC, using a SEM-
Hitachi S3500N electron microscope.
D
B
A
C
209
Illustration D.2. Overview of 42 bermudagrass cultivars from the 2002 National
Turfgrass Evaluation Program located at the Clemson University field research plots.
210
Illustration D.3. Spring green-up comparison of „Riviera‟ (left) and „Tifway‟ (right)
bermudagrass selected from the 2002 National Turfgrass Evaluation Program at the
Clemson University field research plots. Image recorded: 18 April 2006.
Illustration D.4. Spring green-up comparison of „Midlawn‟ (left) and „Celebration‟ (right)
bermudagrass selected from the 2002 National Turfgrass Evaluation Program at the
Clemson University field research plots. Image recorded: 14 April 2007.
211
Illustration D.5. Percent dormancy comparison of „Aussie Green‟ (top-left), „Celebration‟
(top-right), and „TifSport‟ (bottom) bermudagrass selected from the 2002 National
Turfgrass Evaluation Program at the Clemson University field research plots. Image
recorded: 21 November 2006.
212
Illustration D.6. Overview of a greenhouse study investigating the impact of shade on 42
bermudagrass cultivars at the Clemson University greenhouse complex.
213
Illustration D.7. „Tifway‟ (a), „TiftNo.4‟ (b), and „Celebration‟ (c) bermudagrass
response to 5 weeks of 64% continuous shade at the Clemson University greenhouse
research complex.
A
C
B
214
Illustration D.8. Root biomass of Celebration (left) and Tifway (right) bermudagrass
following 8 weeks of 55% continuous shade at the Clemson University greenhouse
complex.
215
Illustration D.9. Overview of a shade structure to investigate the response of
bermudagrass spring transition impacted by 55% continuous shade located at the
Clemson University field research plots.
216
Illustration D.10. Comparison of „Celebration‟ grown under full-sunlight (a) and 55%
continuous shade (b), TiftNo.4 grown under full-sunlight (c) and 55% continuous shade
(d) and „Tifway‟ grown under full-sunlight (e) and 55% continuous shade (f) adjacent to
the Clemson University field research plots.
D
B
C
A
E F
217
Illustration D.11. Spring performance comparison of „TifEagle‟ bermudagrass treated
with a colorant (left) and untreated (right) in the winter grown under full-sunlight. Image
recorded on May 1, 2007.
Illustration D.12. Spring performance comparison of „TifEagle‟ bermudagrass
overseeded in the winter grown in full-sunlight (left) and 55% continuous shade (right).
Image recorded on May 1, 2007.
218
Illustration D.13. Overview of „Champion‟ bermudagrass shade study at the Clemson
University field research plots.
219
Illustration D.14. „Champion‟ bermudagrass response to 147 (a), 294 (b), and 441 (c) kg
a.i. ha-1
yr-1
of nitrogen (urea) when grown under 55% continuous shade for 8 weeks at
the Clemson University field research plots.
A B
C
220
Illustration D.15. „Champion‟ bermudagrass response to 147 kg a.i. ha-1
yr-1
of nitrogen
(urea) with TE (0.02 kg ha-1
2wk-1
) (a) and 294 kg a.i. ha-1
yr-1
of nitrogen (urea) without
TE (b) when grown under 55% continuous shade for 8 weeks at the Clemson University
field research plots.
A B
221
Illustration D.16. Overview of a greenhouse study investigating the impacts of different
light spectral qualities on various warm-season turfgrasses at the Clemson University
greenhouse complex.
222
Illustration D.17. Root biomass comparison of „Sea Isle 2000‟ seashore paspalum (top-
left), „Celebration‟ bermudagrass (top-right), „Tifway‟ bermudagrass (bottom-left) and
„Diamond‟ zoysiagrass (bottom-right) grown under full-sunlight for eight weeks in the
Clemson University greenhouse complex. Image recorded: 13 June 2007.
223
Illustration D.18. Visual quality comparison of „Diamond‟ zoysiagrass (top-left), „Sea
Isle 2000‟ seashore paspalum (top-right), „Celebration‟ bermudagrass (bottom-left),
„Tifway‟ bermudagrass (bottom-right) grown under blue shade for six weeks in the
Clemson University greenhouse complex. Image recorded: 20 August 2007.
224
Illustration D.19. Overview of „L93‟ creeping bentgrass putting green shade study
initiated at the Clemson University field research plots.
225
Illustration D.20. „L93‟ creeping bentgrass response to rolling traffic at 0700 (a) and
rolling traffic at 0900 (b) at the Clemson University field research plots.
A B
226
Illustration D.21. „L93‟ creeping bentgrass response to rolling traffic at 0700 (a) and foot
traffic at 0700 (b) at the Clemson University field research plots.
A B
227
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