Microbial symbionts inhabit tissues of all plants and animals. Their community composition depends largely on two ecological processes: (1) filtering by abiotic conditions and host species determining the environments that symbionts are able to colonize and (2) dispersal-limitation determining the pool of symbionts available to colonize a given host and community spatial structure. In plants, the above- and belowground tissues represent such distinct habitats for symbionts that we expect different effects of filtering and spatial structuring on their symbiont communities. In this study, we characterized above- and belowground communities of fungal endophytes—fungi living asymptomatically within plants—to understand the contributions of filtering and spatial structure to endophyte community composition. We used a culture-based approach to characterize endophytes growing in leaves and roots of three species of coastal beachgrasses in dunes of the USA Pacific Northwest. For leaves, endophyte isolation frequency and OTU richness depended primarily on plant host species. In comparison, for roots, both isolation frequency and OTU richness increased from the nutrient-poor front of the dune to the higher-nutrient backdune. Endophyte community composition in leaves exhibited a distance-decay relationship across the region. In a laboratory assay, faster growth rates and lower spore production were more often associated with leaf- than root-inhabiting endophytes. Overall, our results reveal a greater importance of biotic filtering by host species and dispersal-limitation over regional geographic distances for aboveground leaf endophyte communities and stronger effects of abiotic environmental filtering and locally patchy distributions for belowground root endophyte communities.
Bibliographical noteFunding Information:
We thank D. Asson, S. Gerrity, Y. Kim, P. Lenz, and A. Pradeep for field and laboratory assistance and S. Hacker and J. Spatafora for providing laboratory resources and advice at Oregon State University. We also thank P. Kennedy, L. Kinkel, and D. Tilman for their feedback on this manuscript. We thank the U.S. Fish and Wildlife Service, Oregon Parks and Recreation Department, and Washington State Parks and Recreation Commission for granting us permits to conduct this research. This work was funded by the United States Environmental Protection Agency (EPA/NCER R833836) to EWS, NSF Dimensions of Biodiversity (1045608) to GM, National Science Foundation Integrative Graduate Education and Research Traineeship (NSF-IGERT) Introduced Species and Genotypes program (DGE-0653827), NSF Graduate Research Fellowship program (NSF 00039202), and University of Minnesota Rothman Fellowship to ASD.
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- Community assembly
- Environmental drivers
- Spatial structure