The tall fescue (Lolium arundinaceum)-fungal endophyte (Neotyphodium coenophialum) symbiosis has some agronomic advantages, but it can also be detrimental to the health of grazing animals.  Therefore, efforts have been made to find strains of the endophyte unable to produce the ergot alkaloids known to cause many of the observed grazing animal disorders resulting from this symbiosis.  This effort has resulted in several novel, non-ergot alkaloid producing, endophyte genotypes being recently introduced; however, the influence of these novel endophytes on ecosystem processes is currently unknown.

Here we report the effect of three symbiont fungal genotypes on plant community composition and trace gas fluxes of tall fescue stands over a one year study period. For one variety of tall fescue (PDF, Noble Foundation), we had plots of common toxic endophyte infected (CTE+), two novel endophyte genotypes (AR-542, AR-584) infected, endophyte free (E-), and a mixture of all of endophyte statuses together (MIX). Tall fescue cover and total grass biomass were significantly lower in E- than CTE+, AR-542, AR-584 and MIX, but no significant differences among endophyte genotypes and/or MIX were found. Forb biomass cover and plant species richness were greatest in E- plots, lowest in CTE+, and intermediate for AR-542, AR-584, and MIX plots. All of these plant community effects were strongly seasonal and were more significant in fall than spring.

Endophyte genotype also significantly influenced soil CO₂ and N₂O flux, as higher fluxes were observed from AR-542 compared to the other treatments. Soil NH₃ volatilization was affected by endophyte presence but not by endophyte genotype. Significantly higher soil NO₃^--N contents were found from AR-584 than rest of treatments. However, soil NH₄⁺-N concentration was not influenced by endophyte presence or genotype. In summary, fungal endophyte presence and genotype significantly affected tall fescue pasture species richness, grass biomass, and soil trace gas fluxes, suggesting that endophyte identity is important in understanding the ecosystem-scale effects of this agronomically important grass-fungal symbiosis.