Rapid differentiation of soil-borne plant pathogen and bacteria communities in response to prairie plant community manipulation field experiment

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Haley M Burrill and Guangzhou Wang, Ecology and Evolutionary Biology, The University of Kansas, Lawrence, KS, James D. Bever, Ecology and Evolutionary Biology, University of Kansas, Lawrence, KS

Background/Question/Methods
Plant microbiome divergence can drive both positive and negative plant-soil feedbacks. Accumulation of host-specific pathogens can limit productivity at low plant diversity, thereby allowing establishment of other plant species and diversity maintenance. In high diversity plant communities, reduced abundance of individual plant species and/or an increase in microbial diversity may inhibit pathogen accumulation, allowing greater productivity. Closely related plant species are likely to share pathogen specialists, as well as mutualists such as arbuscular mycorrhizae (AMF) and rhizobia. To better understand the role of microbial dynamics in plant community structure, fungal, AMF, bacteria, and oomycete composition was analyzed from plots planted with combinations of 18 prairie plant species from three plant families: Poaceae, Fabaceae, and Asteraceae. Plots ranged in species richness 1, 2, 3, or 6; either representing multiple families or one family. Plots were initially inoculated with soil from a nearby remnant prairie. Four months after planting, soil samples were collected, and soil and root DNA extracted. We amplified and sequenced rDNA regions targeting fungal, oomycete, AMF, and bacteria communities and processed amplicons using bioinformatics pipelines specific to each group. We tested whether community composition and diversity of each microbial group responded to plant composition, species richness, and phylogenetic dispersion.
Results/Conclusions
There was generally stronger divergence of plant pathogens than saprophytic groups. Fungal plant pathogen species richness increased with planted species richness (p=0.03), total fungal richness did not. Composition of fungal pathogen, oomycete, and bacterial communities diverged significantly with plant family and plant species planted within the plots (p=0.05; p=0.06; p=0.001), while AMF composition and fungal saprophytes were not affected or had reduced responses to plant composition. We identified several taxonomic groups of fungal pathogens that increase or decrease in response to plant family, consistent with plant families sharing host-specific pathogens. In addition, we found rhizobia diversity to increase marginally with the presence of legumes (p=0.09). These results support previous research suggesting that rapid divergence of host-specific plant pathogens can drive negative plant soil feedbacks and thereby influence plant community structure. Our observation of shared pathogens between plant families are consistent with previous research showing weaker negative feedbacks between phylogenetically similar plant species. Rapid accumulation of rhizobia on legumes could also generate positive feedback between legumes and other plant families. Together these microbiome dynamics could mediate the increase in plant productivity with increasing plant species richness and with increasing phylogenetic dissimilarity observed in these plots.