A key aboveground fungal symbiont increases root endophyte richness in a changing world

Background/Question/Methods

Plant-associated fungi have vital effects on host plant ecology, yet mechanisms that structure these symbiont communities are not well-understood. Vertically-transmitted, systemic Clavicipitaceous endophytes, such as those in the genus Epichloë, are known to have particularly strong effects on co-occurring fungal symbionts, including root endophyte communities which can play important roles in plant growth, pathogen defense, and rhizosphere interactions. Rising atmospheric nitrogen (N) deposition associated with anthropogenic activities may enhance dominance of systemic endophytes, and may also directly reduce diversity of root endophyte communities by increasing dominance of strong competitors, similar to patterns seen in plant communities. In this study, we examined the effects of the systemic endophyte Epichloë amarillans on root endophyte communities in the host plant Ammophila breviligulata (American beach grass). Ammophila is native to Great Lakes sand dunes, and acts as an ecosystem-engineer, stabilizing moving sand during early stages of dune succession. In 2020, we collected Ammophila roots from 60 2m x 2m plots that were part of a factorial field experiment manipulating both Epichloë (presence or absence) and N availability (3 levels of fertilizer) in Michigan, USA. We used culture-based and molecular techniques (Sanger sequencing) to characterize changes in fungal root endophyte communities associated with these treatments.

Results/Conclusions

Across all root samples, we isolated more than 130 morphospecies which were later clustered into operational taxonomic units. The presence of Epichloë in Ammophila was associated with, on average, an 11% increase in root endophyte richness but did not influence overall root endophyte community composition. N addition also increased root endophyte richness, specifically in E- plants, and reduced variability in root endophyte community composition across plots. Our results suggest that Epichloë may change host chemical or physical traits in ways that promote higher diversity or abundance of fungal root endophytes, for example by increasing total root area. Increased atmospheric N deposition associated with urbanization and agriculture homogenizes communities, potentially by increasing dominance of competitive taxa. Such interactions between above- and belowground fungal symbionts in plants may have implications for how plants respond to a changing world.