Tall Fescue-Epichloë Coenophiala Associations Affect Belowground Fungi and Host, Symbiont Response to Climate Change.

Plants interact with myriad microorganisms, which influence ecosystem processes and can regulate ecosystem response to global change. One important symbiosis occurs between the grass, tall fescue (Schedonorus arundinaceus), and the asexual fungal endophyte Epichloë coenophiala. Because the common toxic endophyte (CTE) strain harms grazing livestock, non-livestock toxic endophyte (NTE) strains are increasingly deployed in pastures. Little is known about how these symbioses impact other plant-microbe-soil interactions in grasslands or how these relationships will respond to climate change.

Utilizing a climate change study, where grassland plots were subjected to factorial combinations of increased heat (+3°C, year-round) and precipitation (+30% of long-term annual mean precipitation), we planted cloned pairs of two tall fescue genotypes and subjected them to two years of climate manipulation. Within a clone pair, one individual was endophyte-infected (either CTE+ or NTE+) and the other was endophyte-free (CTE- or NTE-). We investigated how belowground fungal symbioses were altered by tall fescue-E. coenophiala genetics and climate change treatments by measuring root arbuscular mycorrhizal fungi (AMF) and fungal dark septate endophyte (DSE) colonization and estimated length of extraradical AMF hyphae (ERH) in soils via microscopy. We hypothesized that 1) unique combinations of host and endophyte genotypes differentially affect belowground fungal colonization, and 2) these associations would be impacted by warming and added precipitation.

AMF arbuscules and vesicles and ERH were significantly affected by tall fescue genotype, endophyte status, and climate change treatments. Root DSE were reduced by endophyte presence but stimulated by warming. Genetically distinct E. coenophiala-tall fescue associations may have divergent long-term impacts on other host-symbiont interactions and belowground communities under future climate change conditions.