why reproductive efficiency in junipers is so low? facts and hypothesis seed ecology 2004 an...

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


J. communis J. hemisphaerica

J. oxycedrus J. phoenicea J. thurifera J. sabina

J. nana

Distribution of Juniperus in Italy


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


Juniperus seed structure

Outer hard integument

Inner papyraceous integument

endosperm

embryo


Fruit germination in nature


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


Collelungo - 36.75.8a -

Migliarino - 46.715.3a-

P. Cavalleggeri - 50.017.3a -

Casciano di M. - 6.711.5 b -


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


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


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


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


Male (left) and female (right) J. communis cones at pollination.

A B


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


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


J. oxycedrus subsp. oxycedrus female cones with the pollination drops (left) and just after pollination (right)


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


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


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




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


Viable pollen

Unviable pollen

Pyrus comm. pollen62 µm

Silica gel 10-15 µm



No retraction x x

Partial retraction

x x

Complete retraction

x x


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


why reproductive efficiency in junipers is so low? facts and hypothesis seed ecology 2004 an...

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