why reproductive efficiency in junipers is so low? facts and hypothesis seed ecology 2004 an...
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WHY REPRODUCTIVE EFFICIENCY IN JUNIPERS
IS SO LOW? FACTS AND HYPOTHESIS
SEED ECOLOGY 2004 an International Meeting on Seeds and the
EnvironmentRhodes Island, Greece (April 29th - May 4th 2004).
Jill Barbour – United States Department of Agriculture - Forest Service - National Tree Seed Laboratory – USA
Serena Mugnaini - Massimo Nepi - Ettore Pacini - University of Siena - Department of Environmental Sciences – Italy
Beti Piotto - APAT Agency for the protection of the environment and for technical services – Department of Nature Protection – Italy
Juniperus Seed Collection Juniperus Seed Collection ProblemsProblems
• Native seed collections contain many Native seed collections contain many empty seedsempty seeds
• Unpredictable and variable seed crops Unpredictable and variable seed crops due to harsh weather conditions due to harsh weather conditions
• Seed maturation periods vary by Seed maturation periods vary by species- immature and mature seed species- immature and mature seed easily mixed together during collection easily mixed together during collection
• Western species in remote areas-Western species in remote areas-inaccessible for easy collectioninaccessible for easy collection
• Equipment for removal of empty and Equipment for removal of empty and low vigor seed not affordable by all low vigor seed not affordable by all processorsprocessors
APAT – Università di Siena – USDA Forest Service
Juniperus Seed Germination Problems
• Complex dormancies - embryo, endosperm, seedcoat, secondary dormancy
• Long stratification periods - vary warm and cold cycles
• Seed viability much greater than germination percentages
• Germination unpredictable in laboratory and nursery
• Seed sources may respond differently to stratification treatments due to introgressionAPAT – Università di Siena – USDA Forest Service
US Distribution of Juniperus
J. pinchottii
J. virginiana
J. monosperma
J. scopulorum
J. silicicola
APAT – Università di Siena – USDA Forest Service
J. communis J. hemisphaerica
J. oxycedrus J. phoenicea J. thurifera J. sabina
J. nana
Distribution of Juniperus in Italy
APAT – Università di Siena – USDA Forest Service
Altitudinal distribution of J. communis and J. oxycedrus
J. oxycedrus subsp. macrocarpa
J. oxycedrus subsp. oxycedrus
J. communis
Collelungo (GR)Torre Mozza (GR)San Vincenzo (LI) Marina di GR (GR)
Piana dei Cavalleggeri (GR)Migliarino (PI)S. Rossore (PI)
Casciano di Murlo (SI)Petriolo (GR)Fontazzi (SI)
Montarrenti (SI)Greve (FI)Lecceto (SI)Monteorgiali (SI)
300m
400m
0m
10m
APAT – Università di Siena – USDA Forest Service
Juniperus seed structure
Outer hard integument
Inner papyraceous integument
endosperm
embryo
APAT – Università di Siena – USDA Forest Service
Fruit germination in nature
APAT – Università di Siena – USDA Forest Service
USDA Forest Service National Tree Seed Laboratory
Seed Testing Data 1962-2002
Total Germ
Mean Germ
Wet wt. Moisture
% Seeds/ Mean Viability
Species No. No. % Content %
Purity
kg %
J. monosperma
3 2 39 . . . 76
J. pinchottii 21 9 12 13.2 100 30,616 .
J. scopulorum 113 31 12 9.2 99.3 60,074 64
J. silicicola 7 7 10 11.9 99.3 97,784 .
J. virginiana 489 323 41 8.4 95.8 136,651
71
Collection sites late 2000-early 2001 late 2001-early 2002 late 2002
J. communis Montarrenti 1.61.5a 3.35.8a 23.313.2b
Petriolo 2.02.0a 0 32.213.0b
Greve 1.31.5a 2.71.5a 33.313.2b
J. oxycedrus subsp. oxycedrus
Collelungo - 36.75.8a -
Migliarino - 46.715.3a-
P. Cavalleggeri - 50.017.3a -
Casciano di M. - 6.711.5 b -
J. oxycedrus subsp. macrocarpa
Marina di GR 66.720.8b -
Collelungo - 36.75.8a -
Migliarino - 53.320.8a -
P. Cavalleggeri - 26.711.5a -
After fox ingestion 36.725.2a 33.315.2a -
After boar ingestion 26.715.3a 26.75.8a -
After badger ingestion - 33.320.8a -
Not predated 20.026.5a - -
Seed viability at different periods, treatments
and sites in the Italian Junipers
APAT – Università di Siena – USDA Forest Service
Male-female ratio of the Italian
Junipers species sites % male % female % not evident
J. communis Greve 48.2 51.8 0
Lecceto 45.8 54.2 0
Petriolo 51.3 48.7 0
Montarrenti 41.6 58.4 0
J. oxycedrus subsp. oxycedrus
P.Cavalleggeri 54.8 45.2 0
Collelungo 18.2 9.1 72.7
Casciano 62.1 37.9 0
Migliarino 24.0 40.0 36.0
S. Rossore 40.0 60.0 0
J. oxycedrus subsp. macrocarpa
Torre Mozza 33.3 66.7 0
S.Vincenzo 52.0 48.0 0
P.Cavalleggeri 18.2 9.1 72.7
Collelungo 8.2 20.4 71.4
Migliarino 25.0 33.3 41.7
S.Rossore 14.3 42.9 42.9
APAT – Università di Siena – USDA Forest Service
Male (left) and female (right) J. communis cones at pollination.
A B
APAT – Università di Siena – USDA Forest Service
Mean sugars pollination drop composition in the tree
italian Junipers
species Glucose mg/mlFructose
mg/mlSucrosemg/ml
J. communis 5.03225 26.68465 _
J. oxycedrus subsp. oxycedrus 4.20591 71.21974 0.49843
J. oxycedrus subsp. macrocarpa 3.03134 44.88447 0.34324
APAT – Università di Siena – USDA Forest Service
Pollination drop retraction at different times after conspecific pollination
0 5’ 12’
Experiment performed under a stereo microscope where the pollination drop diameter was measured at different time intervals
APAT – Università di Siena – USDA Forest Service
J. oxycedrus subsp. oxycedrus female cones with the pollination drops (left) and just after pollination (right)
APAT – Università di Siena – USDA Forest Service
APAT – Università di Siena – USDA Forest Service
Micropylar drop volume at different times after pollination in J. communis
and J. oxycedrus subsp. oxycedrus
Treatments Micropylar drop volume (mm3 x 10-3) at different times from pollination
0 min. 30 min. 2 h 19 h
J. oxycedrus October 2001
Low pollen load 32.2 4.9 4.9 0.0
Heavy pollen load 35.2 4.2 1.9 0.0
Heavy dead pollen load 29.8 6.4 6.4 1.9
J. communis pollen (heavy) 29.4 4.9 4.9 1.6
Charcoal dust 43.3 7.5 7.2 3.9
J. communisFebruary 2002
Low pollen load 13.9 1.1 0.7 0.0
Heavy pollen load 61.5 9.4 6.4 2.1
Heavy dead pollen load 60.7 0.2 0.1 0.0
J. oxycedrus pollen (heavy) 20.5 3.0 1.9 0.0
Talcum powder 61.5 1.9 1.9 15.1
APAT – Università di Siena – USDA Forest Service
J. oxycedrus subs. oxycedrus and J. communis retraction with different treatments
(october 2001 and february 2002)
J. Oxycedrussubsp. oxycedrus
No pollinationLow pollen
load
Heavy pollen load
dead pollen Juniperus communis
pollen
charcoal dust
No retraction x
Partial retraction x
Complete retraction x x x x
J. communis No pollinationLow pollen
loadHeavy
pollen loaddead pollen
Juniperus oxycedrus
pollentalcum
No retraction x
Partal retraction x
Complete retraction x x x x
APAT – Università di Siena – USDA Forest Service
Sizes of particles used for artificial pollination experiments
Types of particles Mean size (diameter)
J. oxycedrus subsp. oxycedrus pollen 39 µm
J. oxycedrus subsp. macrocarpa pollen 40 µm
Pyrus communis pollen 62 µm
Parietaria diffusa pollen 25 µm
Silica gel 1 10-15 µm
Silica gel 2 40-63 µm
Silica gel 3 63-200 µm
APAT – Università di Siena – USDA Forest Service
Taxon Type of particlesMicropylar drop volume at different times after
pollination (mm3 x 10-3)
0 min. 30 min. 2 h 19 h
J. oxycedrus subsp. oxycedrusDecember 2002
Unpollinated 13.9 10.8 13.910.8 13.910.8 28.223.9
Viable pollen 18.78.1 3.72.3 3.22.9 0.00.0
Unviable pollen 16.732.0 0.81.8 0.20.5 0.00.0
Pyrus communis pollen 14.322.8 12.723.0 12.123.2 10.015.2
Silica 1 110.6169.7 80.7120.8 77.5122.5 73.2124.4
Silica 2 65.972.5 38.338.7 40.137.8 31.628.8
Silica 3 10.16.0 9.56.5 9.66.4 20.714.7
J. oxycedrus subsp. macrocarpaDecember 2002
unpollinated 53.677.8 54.177.5 54.177.5 72.868.1
Viable pollen 23.724.8 7.18.6 1.31.9 0.50.9
Unviable pollen 22.021.1 2.72.2 2.42.4 2.42.5
Pyrus communis pollen 40.246.4 30.533.7 21.134.5 13.936.4
Parietaria diffusa pollen 12.010.4 12.010.4 11.510.8 11.510.8
Silica gel 1 83.190.2 29.546.8 48.246.8 85.784.3
Silica gel 2 40.447.5 28.339.3 26.739.5 33.377.9
Silica gel 3 22.418.1 13.915.5 11.216.2 20.928.6
J. oxycedrus subsp. oxycedrus micropylar drop
retraction after different treatments
J. oxycedrus subsp. oxycedrus
Viable pollen
Unviable pollen
Pyrus comm. pollen62 µm
Silica gel 10-15 µm
Silica gel 40-63 µm
Silica gel 63-200 µm
No retraction x x
Partial retraction
x x
Complete retraction
x x
APAT – Università di Siena – USDA Forest Service
CONCLUSIONS
1. This research confirms a low germination rate of junipers seeds independently of the species and the environments where they live.
2. The pollination drop system is a weak point in the reproductive cycle because easily deceived by:
a) heterospecific pollen
b) its unviable pollen
c) atmospheric dust increased during the last decades
3. Gymnosperms with pollination drops seem not very well fitted with the actual environment.
4. Angiosperms with stigmatic pollination are probably better adapted to the present environment, but this must be demonstrated
APAT – Università di Siena – USDA Forest Service
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