COS 28-1 - Environmental filtering by soil moisture and dispersal limitation as drivers of endophytic fungal community assembly in Schizachyrium scoparium

Background/Question/Methods

Despite the importance of microbial symbiont communities (the “microbiome”) to host growth and reproduction, we lack a clear understanding of the fundamental processes by which these communities assemble within the host. Here, we ask the importance of deterministic processes such as environmental filtering, and neutral processes such dispersal limitation, to the assembly of root endophytic fungal communities associated with the iconic prairie grass, little bluestem (Schizachyrium scoparium) across a 900 km geographic gradient of mean annual precipitation (MAP). We characterized communities using Illumina community sequencing of the fungal barcode rDNA for replicate root samples across 10 native prairie sites from Kansas to Minnesota. We compared the richness, composition and the phylogenetic structure of these root endophytic fungal communities to make inferences regarding the role of environmental filtering and dispersal limitation on community assembly.

Results/Conclusions

Our results show that root endophytic fungi constitute a tremendously diverse community, with an average of 75 taxa per plant and 580 taxa per site and region. Overall, we found that the similarity in the composition of root endophytic fungal communities gradually decreases with geographic distance and the MAP gradient, suggesting that both dispersal limitation and environmental filtering play a role in structuring these communities. Further, our results show that root endophytic fungal community composition significantly varies within sites, suggesting that environmental heterogeneity at smaller spatial scales maintains the high species diversity we observe. The soil moisture environment may generate selection and differently affect diverse fungal symbiotic species as we found that the relative abundance of key endophytic fungal species correlates with MAP, suggesting that different fungal species may adapt to either high or low moisture environments. Together, our results provide strong evidence that both deterministic (environmental filtering, adaptation) and stochastic processes (dispersal limitation) contribute to microbial symbiont community assembly. Further, given the significant variation in root endophytic fungal community composition with soil moisture, our results imply that anthropogenic climate change would likely disrupt the stability of microbial symbiont communities associated with prairie plants.