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Division S-3—Soil Biology & Biochemistry

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

^a USDA-ARS, 1420 Experiment Station Road, Watkinsville, GA 30677-2373
^b Dep. of Crop and Soil Sciences, Univ. of Georgia, Athens, GA 30602-7272

^* Corresponding author (afranz{at}uga.edu)

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.

Abbreviations: E–, endophyte free • E+, endophyte infected • SOC, soil organic carbon