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

Allelopathic Influences of Oak and Eucalyptus on Allelopathy is an interference the Vegetation of the mechanism in which live or Elkhorn Slough dead plant materials release chemicals which have a direct or indirect effect on herbivores, pathogens, and other plants. How Does it Work? 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, Plant B: Plant A: and terpenes Allelochemicals Allelochemicals absent present How Does it Work? Functions of secondary products • Act as signals in response to environmental cues • Provide protection against solar radiation • Aid in pollen and seed dispersal • Defense against herbivores, pathogens, Plant B: Plant A: and other plant competitors Allelochemicals Allelochemicals absent present

How Does it Work? How Does it Work? Plant B: Plant B: Plant A: Plant A: Allelochemicals Allelochemicals Allelochemicals Allelochemicals absent absent present present How Does it Work? How Does it Work? Plant B: Plant B: Plant A: Plant A: Allelochemicals Allelochemicals Allelochemicals Allelochemicals absent absent present present 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 Plant B: Plant A: leachate Allelochemicals Allelochemicals absent present

Allelopathic compounds • Oaks produce mostly tannins, which are a sub-group of phenolics The Growing Structure • Eucalyptus produce several compounds, mostly terpenes and phenolics Seed bank composition 40 35 Total plants germinated 30 Seed bank 25 Euc 20 Oak 15 comparison 10 5 0 m s s s m a a s s r s i u u v u u s e l i t u a l r a h a i l a n h e l a i g a d r t h a i c p M l g o a G o h o n p n y f p p o n n e r A C e a o S w w c R n o P o o e n a n n h c k k t y C i n n n p U U o s M u u d r a C Sample collection 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

Seed bank results: Effect of same source leachate Leachate Oak 1A seed Eucalyptus 1A bank seed bank 12 12 Mean seeds germinated effects on 10 10 8 8 6 6 seed bank 4 4 2 2 0 0 DI Euc DI Oak Somewhat significant for Euc p = 0.091 Two-way ANOVA Drip method Leachate leachate extraction effects on indicator seeds Seed bank in 50% shade Concentrated leachate Same source leachate De-ionized water extraction Euc Oak Euc Oak

Germination in Petri dishes Germination of Achillea millefolium 22.5 On paper: Day 9 On soil: Day 13 Mean seeds germinated 20 17.5 15 12.5 10 10 7.5 8 6 5 4 2.5 2 0 0 DI Euc Oak DI Euc Oak Significant for Oak p = 0.0040 Euc p = <0.0001 Two-way ANOVA Germination of Germination of Mimulus aurantiacus Bromus maritimus On filter paper: Day 9 On filter paper: Day 9 On soil: Day 13 10 25 25 Mean seeds germinated 22.5 22.5 Mean seeds germinated 8 20 20 17.5 17.5 6 15 15 12.5 12.5 4 10 10 7.5 2 7.5 5 5 0 2.5 2.5 DI Euc Oak 0 0 Euc DI Oak Significant for DI Euc Oak Oak p = 0.0059 Significant for Oak Euc p = 0.0059 Two-way ANOVA p = 0.043 Two-way ANOVA Germination of Baccharis Conclusions On soil: Day 13 On filter paper: Day 9 •Seedbank composition: common 18 18 dominants, and same level of diversity 16 16 Mean seeds germinated 14 14 •Eucalyptus and oak weakly suppress 12 12 natural seed bank germination 10 10 8 8 •Different species have different 6 6 responses to leachate exposure 4 4 2 •For some species, the soil may buffer 2 0 0 the interference mechanism DI Euc Oak DI Euc Oak Two-way ANOVA

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.