Functions of secondary products Act as signals in response to - - PDF document

Allelopathic Influences of Oak and Eucalyptus on the Vegetation of the Elkhorn Slough

Plant chemical compounds

• Primary products: found in all plant

cells, necessary for survival

• Secondary products: restricted in

their distribution, both within the plant and among different species

• Includes alkaloids, phenolics,

and terpenes

• Act as signals in response to

environmental cues

• Provide protection against solar radiation
• Aid in pollen and seed dispersal
• Defense against herbivores, pathogens,

and other plant competitors

Functions of secondary products

Allelopathy is an interference mechanism in which live or dead plant materials release chemicals which have a direct

• r indirect effect on

herbivores, pathogens, and

• ther plants.

Plant A: Allelochemicals present Plant B: Allelochemicals absent

How Does it Work?

Plant A: Allelochemicals present Plant B: Allelochemicals absent

How Does it Work?

Plant A: Allelochemicals present Plant B: Allelochemicals absent

How Does it Work?

Plant A: Allelochemicals present Plant B: Allelochemicals absent

How Does it Work?

Plant A: Allelochemicals present Plant B: Allelochemicals absent

How Does it Work?

Plant A: Allelochemicals present Plant B: Allelochemicals absent

How Does it Work?

Plant A: Allelochemicals present Plant B: Allelochemicals absent

How Does it Work?

My research:

• Investigated the direct effect of

allelochemicals derived from the leaf litter of Quercus agrifolia and Eucalyptus globulus on native and non-native understory plants

• Carried out a series of germination

experiments, in which seeds were exposed to varying light intensity, substrate composition, and concentrations of leaf litter leachate

Allelopathic compounds

• Oaks produce mostly tannins,

which are a sub-group of phenolics

• Eucalyptus produce several

compounds, mostly terpenes and phenolics

Seed bank comparison

Sample collection

The Growing Structure

Seed bank composition

5 10 15 20 25 30 35 40 A n a g a l i s C a r d u u s p y c n

• c

e p h a l i s C y p e r u s G a l i u m M a l v a M

• n

i t a P e r f

• l

i a t a R a p h a n u s C h e n

• p
• d

i u m S

• n

c h u s U n k n

• w

n g r a s s U n k n

• w

n

• t

h e r Total plants germinated Euc Oak

Sax, 2002

• Showed similar species richness

and diversity for oak and eucalyptus understory plants

• Majority of species sampled did

not occur in both woodland types, with only 39% in common between the two

Leachate effects on seed bank

Drip method leachate extraction Seed bank in 50% shade

Euc Oak Euc Oak Same source leachate De-ionized water

Seed bank results: Effect of same source leachate

Eucalyptus 1A seed bank Oak 1A seed bank

2 4 6 8 10 12 DI Euc 2 4 6 8 10 12 DI Oak Mean seeds germinated

Somewhat significant for Euc p = 0.091

Two-way ANOVA

Leachate effects on indicator seeds

Concentrated leachate extraction

Germination in Petri dishes

On filter paper: Day 9

Mean seeds germinated 2.5 5 7.5 10 12.5 15 17.5 20 22.5 25

DI Euc Oak

On soil: Day 13

2.5 5 7.5 10 12.5 15 17.5 20 22.5 25 DI Euc Oak

Germination of Bromus maritimus

Significant for Oak p = 0.043

Two-way ANOVA

On filter paper: Day 9

2 4 6 8 10 12 14 16 18 DI Euc Oak

On soil: Day 13

2 4 6 8 10 12 14 16 18 DI Euc Oak

Germination of Baccharis

Mean seeds germinated Two-way ANOVA

On paper: Day 9 On soil: Day 13

Germination of Achillea millefolium

Mean seeds germinated 2.5 5 7.5 10 12.5 15 17.5 20 22.5 DI Euc Oak 2 4 6 8 10 DI Euc Oak

Significant for Oak p = 0.0040 Euc p = <0.0001

Two-way ANOVA

On filter paper: Day 9

2 4 6 8

10

DI Euc Oak

Germination of Mimulus aurantiacus

Significant for Oak p = 0.0059 Euc p = 0.0059

Mean seeds germinated Two-way ANOVA

Conclusions

• Seedbank composition: common

dominants, and same level of diversity

• Eucalyptus and oak weakly suppress

natural seed bank germination

• Different species have different

responses to leachate exposure

• For some species, the soil may buffer

the interference mechanism

Future questions

• Experiment with different understory

plant species

• Manipulate the leachate concentrations
• Explore leachate chemical composition
• Assess and modify the light intensity
• Adjust the leaf litter thickness
• Consider a broader geographic scope

Special thanks to:

Jill Bushakra Kerstin Wasson ESNERR Cabrillo College Chemistry Department S & S Seeds, Inc.