Do multiple aboveground fungal endophyte genotypes similarly affect belowground arbuscular mycorrhizal fungal colonization of tall fescue roots and associated plant and soil parameters?
Tall fescue (Schedonorus arundinaceus Schreb.), a cool-season grass prevalent throughout the eastern U.S., often hosts an aboveground fungal endophyte, Epichloë coenophiala, which functions as a defensive mutualist, improving tall fescue’s environmental stress resistance and competitive ability. Association with the ergot alkaloid-producing common toxic endophyte (CTE) strain of E. coenophiala has been shown to inhibit tall fescue root colonization by arbuscular mycorrhizal fungi (AMF), which are important and widespread belowground fungal symbionts. However, other non-ergot-producing E. coenophiala strains, so called novel, non-toxic endophytes (NE), have been identified, and although acreage of NE-infected tall fescue is increasing, no studies have investigated whether NE strains produce similar tripartite interactions between the plant host, the endophyte, and AMF. At a field site containing 5-year old plots of tall fescue that were either: 1) endophyte-free (E-), 2) CTE-infected (CTE+), or NE-infected by two different novel endophyte strains, 3) AR542 NE+ or 4) AR584 NE+, we asked whether all strains of E. coenophiala similarly influenced tall fescue root colonization by AMF and associated plant and soil characteristics. We quantified root %AMF colonization and plant N and P concentrations, as well as soil extraradical AM hyphae, aggregate stability, and C content.
Neither presence nor strain of E. coenophiala significantly affected tall fescue root AMF colonization rates, although a tendency for decreased colonization within CTE+ tall fescue was observed. Endophyte treatments also produced no significant differences in root and shoot nutrient concentrations or size and stability of soil aggregates. However, tall fescue shoot % P was found to negatively correlate with root AMF colonization (R2 = 0.25, p = 0.01), suggesting that plants invested less in AMF colonization as plant P limitation was reduced. The lack of an endophyte effect on tall fescue AMF colonization directly contrasts with prior greenhouse study findings, and suggests that environmental conditions at our field site, perhaps relatively mesic climatic conditions, facilitated non-antagonistic interactions between these two groups of fungal symbionts. The fact that all strains of the aboveground endophyte behaved similarly, with no inhibition of AMF colonization or alteration of associated plant and soil properties, suggests that replacement of CTE- with NE-infected tall fescue may not have substantial belowground ecosystem effects, at least in this region of the U.S.