Abstract: Foliar fungal endophytes (FFE) form diverse communities in plant leaves, and can influence a wide variety of host functions. FFE community assembly is driven by a variety of both stochastic and deterministic factors, including dispersal limitation, environmental variation, and host taxon. However, distinguishing their relative influence is challenging, given that they are often confounded in natural contexts, and as such, there is a significant lack of intensive field studies on FFE in wild plant communities. In this study, we aimed to address this gap with a field survey of FFE in Clarkia xantiana (Onagraceae), an annual wildflower native to a small stretch of the southern Sierra Nevada foothills in California. This species occurs across a narrow but highly heterogeneous environment, thus allowing us to uncouple the influence of spatial and environmental distance. We took leaf samples from 10 individuals in 50 populations of C. xantiana across its 80km range in the Kern River Canyon. We also sampled the more distantly related annual Marah horridus (Cucurbitaceae) at every site, and a congener, C. unguiculata, at each of the sites where it co-occurred, a subset of 20. We used ITS1 amplicon sequencing to characterize the fungal communities of each host species at each site. The environmental variables we examined were annual precipitation, annual mean temperature, Enhanced Vegetation Index (EVI), solar radiation, and soil type. Preliminary results suggest that the relative influence of spatial vs environmental distance on FFE community assembly differs among host species. Community similarity among sites was significantly correlated with spatial distance for C. unguiculata, but was not for C. xantiana or M. horridus. Analyses on the relationship between community similarity and environmental variation will be completed this spring, and will allow us to explicitly compare how the relative influence of spatial vs environmental distance varies among hosts. We will also be able to identify which environmental factors explain the most variation in FFE community similarity, and if this also varies among host species. Ultimately, this study will provide important context on not only the relative role of spatial & environmental variation in FFE community assembly, but also if this is consistent among host taxa, an important consideration for the generalizability of future studies.
