The influence of pathogen diversity and resource heterogeneity on plant diversity.
Bradley, Devon*,1, Gilbert, Gregory2, Hughes, Jennifer1, 1 Brown University, Providence, RI, United States2 University of California Santa Cruz, Santa Cruz, CA, United States
ABSTRACT- The staggering diversity and abundance of disease-causing microbes associated with plants suggests that plant diseases may influence plant community dynamics. Specifically, it has been hypothesized that an increase in pathogen diversity increases plant diversity. However, the extent to which pathogen diversity, relative to other factors, influences the overall diversity and composition of plant communities has yet to be determined. We investigated the relative influence of pathogen diversity and nutrient heterogeneity on plant diversity using a model community of four Brassica species, a fungal pathogen, and a bacterial pathogen. We examined the hypothesis that increased pathogen diversity increases plant diversity by exposing the mixed Brassica communities to a number of pathogens (none, one, or two). Additionally, the mixed communities were grown in either a homogenous or heterogeneous resource environment to test the influence of pathogen diversity relative to resource heterogeneity. For multiple generations, we tracked community composition and the proportion of diseased plants, and measured seed number and seed weight. After just one generation, we found significantly different rates of infection among the 4 Brassica species, suggesting that the two pathogens had differential effects on fecundity of host species. Furthermore, there was a significant shift in plant community diversity by the second generation. The plant communities grown in the absence of disease were significantly less diverse than diseased communities and plant communities infected with two pathogens maintained the greatest number of species. In contrast, we have not found a difference in plant diversity between communities receiving homogenous or heterogeneous nutrients. However, we expect that the influence of resource heterogeneity may become important in the third and fourth generations and may ultimately interact with pathogen diversity to increase plant community diversity.
Key words: pathogens, diversity, Brassica, resource heterogeneity
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