Phosphorus source and Epichloë coenophiala strain interact over time to modify tall fescue rhizosphere microbial community structure and function

Symbiosis between the fungal endophyte Epichloë coenophiala naturally found in the cool season grass tall fescue (Lolium arundinacea (Schreb) Darbysh.) is thought to provide a competitive advantage over endophyte-free grasses when grown under nutrient-limited conditions. The mechanisms involved in the purported improvement in phosphorus (P) uptake due to endophyte infection are still not understood. The present study tested the influence of endophyte strain and soil P form on P uptake. Plants were grown in acid, low-P soils and those same soils spiked with 30 mg P kg⁻¹ of FePO₄ or AlPO₄. Soil P transformations, acid phosphatase activity, and soil microbial community composition were measured in rhizosphere soils of tall fescue infected with novel (AR542E+ and AR584E+) and common toxic fungal endophytes (CTE+) at 45, 90 and 135 days and compared to endophyte free (E−) tall fescue. We found that endophyte strain (notably AR542E+) had a distinct influence on plant biomass production and lesser P availability increased the endophyte specific effects on rhizosphere biogeochemical properties in a time and endophyte-dependent manner. Shoot specific endophytes had a greater effect on rhizosphere general fungi under P limiting conditions (i.e. control and Fe-Ps). As far as we know, this study provides some of the best evidence to date for shoot-specific fungal endophyte effects on rhizosphere microbial community composition and the roles that nutrient availability and plant development play in modulating this response.