Drivers of grass endophyte communities in prairies of the Pacific Northwest, USA

Prairies of the Pacific Northwest are highly threatened, with only ∼2% of historic land area remaining. The combined risk of global climate change and land use change make these prairies a high conservation priority. However, little attention has been paid to the microbiota of these systems, including the hyper diverse fungi that live asymptomatically in their leaves, the endophytes. Using culture-free, full-community DNA sequencing, we investigated the diversity, composition, and structure of full fungal foliar endophyte and ecological guild communities in two native, cool-season bunchgrasses along a climate gradient. We quantified the relative importance of host, host fitness, environment, and spatial structuring in microbial community structure. We found markedly different communities between the southern and central-northern sites, suggesting a potential dispersal limitation in the Klamath Mountains. We also found that each host species was home to distinct fungal communities. Climate was the strongest predictor of endophyte community, while fitness (e.g., plant size, reproductive status, density) was less important for community structure. For both host species, seasonality contributed strongly to the variation we observed. At the ecological guild level, saprotrophs tended to decline with latitude, whereas symbiotrophs and pathotrophs both tended to increase with latitude. Our results suggest that climate change will have large consequences for these diverse fungal communities.