Leaf endophytes of three annual plants

Foliar fungal endophytes are microbial symbionts that inhabit the leaves of nearly all plant species, but the factors driving their community assembly remain poorly understood. We surveyed endophyte communities associated with three host species across a 100-km environmental gradient in the Sierra Nevada, California, to disentangle the relative influence of dispersal limitation, host filtering, and environmental variation on community composition and diversity. Our results reveal that spatial distance is the primary driver of endophyte community composition, with similarity declining among sites regardless of environmental variation. By contrast, host identity and environmental factors were the predominant predictors of diversity, with one host, Marah fabacea, supporting higher fungal richness and diversity compared to two congeneric Clarkia species. Remarkably, while most fungal taxa were unique to a single host species at the site level, this pattern of host filtering was not consistent at larger spatial scales. Instead, the specific taxonomic composition of endophyte communities appears to be largely determined by dispersal limitation. Our findings highlight the complex interplay of spatial, environmental, and host factors in shaping foliar fungal endophyte communities and emphasize the importance of considering multiple hosts and scales when studying microbial community assembly.