Prescribed fire is frequently used as a tool during restoration of tall fescue pastures to native warm season grassland, and is thought to reduce tall fescue growth and dominance while simultaneously encouraging native grassland species. The majority of tall fescue in these pastures hosts an  aboveground fungal endophyte, Neotyphodium coenophialum. This mutualistic symbiosis is thought to improve the environmental stress tolerance and competitivenesss of host plants (E+) over neighboring uninfected tall fescue (E-) individuals and potentially native grassland species. Specifically, previous research has shown that E+ plants are better able to grow under water-limited conditions, which frequent fire may promote. To assess how fungal endophyte symbiosis interacts with fire and water availability, we used a greenhouse experiment to examine the effects of these three variables (endophyte infection: E+ vs. E-, prescribed fire: 1 burn vs. 2 burn vs. no burn control, and watering regime: dry vs. wet) on tall fescue growth. Treatments were applied in a completely randomized full factorial design, with six replications of each treatment combination. Tiller length was measured over the study period (18 weeks) and final aboveground and belowground biomass was harvested. ANOVA and means comparisons (Tukey-Kramer HSD) were used to detect significant treatment differences (p<0.05).  
Results/Conclusions

Aboveground biomass of tall fescue was uniformly greater in wet vs. dry watering regimes. Within the dry treatment, we found significantly different biomass between E+ and E- tall fescue individuals for the 2 burn treatment only (p=0.017); however, contrary to expectations, E- biomass was  significantly greater than E+. This unexpected reduction in tall fescue biomass with endophyte symbiosis was also observed in the wet treatment, though in the pots burned once (p=0.010) but not those burned twice.  Across both watering regimes, tall fescue growth was enhanced by the 1 burn vs. the 2 burn or control treatments (p<0.001 for both dry and wet). This result suggests that more than one prescribed fire will be required to significantly reduce tall fescue cover in these grassland restorations: even the 2 burn treatment did not reduce tall fescue growth below that of the control in this experiment. Our finding of greater E- tall fescue growth following fire in the dry treatment (compared to E+) is at odds with prior research showing endophyte infection substantially enhances tall fescue growth and recovery following drought.  This puzzling result will require further investigation.