Soil Carbon, Nitrogen, and Ergot Alkaloids with Short‐ and Long‐Term Exposure to Endophyte‐Infected and Endophyte‐Free Tall Fescue

Tall fescue ( Festuca arundinacea Schreb.) is an important cool‐season perennial forage naturally infected with an endophyte, Neotyphodium coenophialum Glenn, Bacon, & Hanlin, which produces ergot alkaloids. We conducted a controlled incubation study to determine the fate of C, N, and ergot alkaloids in tall fescue leaf tissue added to soil. The experimental setup was a factorial combination of endophyte‐free (E−) and endophyte‐infected (E+) leaf tissue (short term) incubated in soil exposed to 10 yr of E− and E+ tall fescue pasture (long term). Soil history of E+ compared with E− reduced C mineralization per unit of soil organic carbon (52 vs. 55 mg g −1 SOC) and the fraction of inorganic N as nitrate (0.68 vs. 0.72 g g −1 ), but increased ergot alkaloid concentrations in soil sediment (<1 mm; 28 vs. 12 ng g −1 ), coarse fraction (>1 mm + remaining leaves; 5.8 vs. 2.2 ng g −1 ), and water extract (0.27 vs. 0.22 ng g −1 soil). Short‐term exposure of soil to E+ leaves compared with E− leaves reduced C mineralization (660 vs. 688 μg g −1 soil) and soil microbial biomass C (487 vs. 583 μg g −1 soil), but increased net N mineralization (70 vs. 59 μg g −1 soil), soil microbial biomass N (56 vs. 19 μg g −1 soil), and ergot alkaloid concentration in the coarse fraction (0.36 vs. 0.27 μg g −1 original leaf). Both short‐ and long‐term exposure of soil to E+ tall fescue were affecting soil organic matter dynamics by altering biochemical transformations of C and N. Our results suggest that wild‐type E+ tall fescue can alter soil organic C storage through a reduction in soil microbial activity. This research has also demonstrated the presence of ergot alkaloids in soil under E+ tall fescue.