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

on tall fescue pastures (West et al., 1988; Clay, 1993; Siegel and Bush, 1996), as well as controlling plant disTall fescue (Festuca arundinacea Schreb.) is an important cooleases (Latch, 1997). A variety of alkaloids, N-containing season perennial forage naturally infected with an endophyte, Neotyphodium coenophialum Glenn, Bacon, & Hanlin, which produces ring structures, are produced in the tall fescue-Neoergot alkaloids. We conducted a controlled incubation study to detertyphodium association (Bush et al., 1993), of which some mine the fate of C, N, and ergot alkaloids in tall fescue leaf tissue may be more important in controlling insect and mamadded to soil. The experimental setup was a factorial combination of malian herbivory and altering plant physiological reendophyte-free (E ) and endophyte-infected (E ) leaf tissue (short sponses to stress. Pyrrolizidine alkaloids can deter insect term) incubated in soil exposed to 10 yr of E and E tall fescue feeding (Johnson et al., 1985). Ergot alkaloids appear pasture (long term). Soil history of E compared with E reduced to be responsible for toxic conditions in cattle (Hill et C mineralization per unit of soil organic carbon (52 vs. 55 mg g 1 al., 1994). Neotyphodium also infects a variety of natural SOC) and the fraction of inorganic N as nitrate (0.68 vs. 0.72 g g 1), grass populations around the world, and in some cases, but increased ergot alkaloid concentrations in soil sediment ( 1 mm; decreases the fitness of plant hosts due to competition 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 for nutrients between plant host and endophyte (Faeth exposure of soil to E leaves compared with E leaves reduced C et al., 2004). mineralization (660 vs. 688 g g 1 soil) and soil microbial biomass C Endophyte associations with tall fescue have been (487 vs. 583 g g 1 soil), but increased net N mineralization (70 vs. recently manipulated, such that strains of fungus with 59 g g 1 soil), soil microbial biomass N (56 vs. 19 g g 1 soil), and low ergot alkaloid production have been selected and ergot alkaloid concentration in the coarse fraction (0.36 vs. 0.27 g combined with improved cultivars of tall fescue (Bouton g 1 original leaf). Both shortand long-term exposure of soil to E et al., 2002). A distinction can now be made between tall fescue were affecting soil organic matter dynamics by altering wild-type endophyte association (occurring naturally biochemical transformations of C and N. Our results suggest that with high ergot alkaloid production) and novel endowild-type E tall fescue can alter soil organic C storage through a phyte association (selected fungus with little or no ergot reduction in soil microbial activity. This research has also demonstrated the presence of ergot alkaloids in soil under E tall fescue. alkaloid production). Pastures in Georgia containing a high occurrence of E tall fescue were found to be associated with greater soil organic C and N concentration and lower potential T fescue is the most widely adapted cool-season soil microbial activity than pastures with low occurrence of perennial forage in the eastern USA (Stuedemann endophyte infection (Franzluebbers et al., 1999). These and Hoveland, 1988). A natural association with a fundata suggested that soil microbial activity might be suffigus (N. coenophialum; formerly called Acremonium ciently reduced by the presence of endophyte metabocoenophialum Morgan-Jones and Gams) often results lites (i.e., various alkaloids and phenolics produced by the in improved persistence of tall fescue in the seasonally endophyte association), as to eventually lead to greater droughtand heat-stressed region of the southeastern accumulation of soil organic C and N due to reduced USA (Hill et al., 1991; Bouton et al., 1993). Reasons decomposition of plant-derived compounds. Support for for its persistence have been attributed to physiological this hypothesis of reduced microbial activity with endoresponses that confer greater drought tolerance (Belesky phyte infection was demonstrated in an outdoor microet al., 1987a; West et al., 1993) and production of ergot cosm study in Argentina, where leaf litter from E alkaloids that may reduce forage intake by grazing aniItalian ryegrass (Lolium multiflorum Lam.) decomposed mals, thereby reducing grazing pressure (Hoveland et slower than E leaf litter (Omacini et al., 2004). al., 1983; Read and Camp, 1986; Hill et al., 1990). Toxic We conducted a controlled incubation study to test effects of E tall fescue on grazing animals, causing the hypothesis that E tall fescue leaves would reduce such disorders as fescue foot, fat necrosis, and fescue C and N mineralization, as well as the agent of many toxicosis, have been well documented (Stuedemann and biochemical transformations in soil, the microbial bioHoveland, 1988; Bacon and Hill, 1997). mass. We tested this hypothesis by exposing soil to endoEcologically, the presence of N. coenophialum may phyte metabolites from fresh tall fescue leaves and from be important in reducing a variety of insect pressures long-term pasture growth. We also tested a hypothesis that soil exposed to endophyte metabolites for many A.J. Franzluebbers, USDA-ARS, 1420 Experiment Station Road, years might condition soil to overcome any reduced Watkinsville, GA 30677-2373; N.S. Hill, Dep. of Crop and Soil Scipotential to decompose freshly added E tall fescue ences, Univ. of Georgia, Athens, GA 30602-7272. Received 22 Mar. 2004. *Corresponding author ([email protected]). leaves. Finally, we wanted to determine the fate and Published in Soil Sci. Soc. Am. J. 69:404–412 (2005). © Soil Science Society of America Abbreviations: E , endophyte free; E , endophyte infected; SOC, soil organic carbon. 677 S. Segoe Rd., Madison, WI 53711 USA