Ecophysiological Responses of Tall Fescue Genotypes to Fungal Endophyte Infection and Elevated Temperature and Precipitation.

Tall fescue (Schedonorus arundinaceus) is a cool-season grass, widely used as a forage species in the eastern USA.  It can form a symbiosis with the fungal endophyte, Epichloë coenophialum, whose presence can benefit the plant, depending on plant and fungal genetics and prevailing environmental conditions.  Despite having agricultural, economic and ecological importance, relatively little is known regarding how the symbiosis will respond to predicted climate change.  Therefore, we quantified the ecophysiological responses of four endophyte-infected (E+) and endophyte-free (E-) tall fescue genotypes to climate change factors, specifically elevated temperature and increased growing season precipitation.  We hypothesized that ecophysiological responses would vary across fescue genotypes and depend on Epichloë presence.  Furthermore, we predicted that endophyte infection would not confer the same degree of environmental stress tolerance to all fescue genotypes.  To assess these predictions, we transplanted four tall fescue genetic clone pairs (where each pair consisted of one E+ and one E- clone) into an existing multi-factor climate change experiment located in central Kentucky.  Each clone pair varied in plant and endophyte genetic material.  Photosynthesis, leaf water potential, tiller number, aboveground biomass and alkaloid concentrations were measured on these individuals from March to November 2012. 

When averaged across the growing season, photosynthesis rates were significantly impacted by elevated heat and increased precipitation but in contrasting ways depending on the fescue genotype and endophyte status.  Often, E+ individuals performed better than E-, except for leaf water potential, which was never influenced by endophyte presence.  Endophyte infection conferred different levels of environmental stress tolerance in the different fescue genotypes.  Overall, this study suggests that choice of plant and endophyte genetic material will be important in determining the productivity and resilience of fescue pastures under future climate conditions.