Interpretive Summary: Tall fescue is an important cool-season perennial forage for cattle production in the humid regions of the USA and throughout the world. Tall fescue is typically infected with an endophytic fungus, which produces alkaloidal compounds within the leaf tissue. These alkaloids cause animal health disorders upon ingestion. We hypothesized that pastures containing these alkaloids may alter soil organic matter dynamics. Soil organic carbon under tall fescue with high endophyte infection was 13% greater than with low endophyte infection. However, potential microbial activity was 14% lower with high than with low endophyte infection. Endophyte infection of tall fescue may have an important ecological function, allowing more soil organic C and N to accumulate, perhaps because of reduced soil microbial activity on plant residues containing endophyte byproducts.
Technical Abstract: While endophyte (Neotyphodium coenophialum) infection of tall fescue (Festuca arundinacea Shreb) results in accumulation of toxic alkaloids in leaf tissue known to cause animal health disorders upon ingestion, it also has many benefits. We hypothesized that pastures containing these alkaloids may alter soil organic matter dynamics. A set of three field experiments representing low endophyte infection (0-20%) and high endophyte infection (60-100%) of tall fescue were evaluated at the end of either 8 or 15 years. Paddocks were grazed yearly with Angus cattle (Bos taurus). Soil samples from a total of 12 paddocks (0.7-0.8 ha) with either low or high endophyte level were collected at depths of 0-25, 25-75, 75-150, and 150-300 mm. Soil under tall fescue with high endophyte infection had 13% greater concentrations of soil organic C and N and particulate organic N to a depth of 150 mm than with low endophyte infection. However with low endophyte infection, microbial biomass and basal soil respiration per unit of soil organic C or particulate organic C were 86% of those with high endophyte infection. Only samll differences in microbial diversity were observed between soils under fescue with 0 and 100% endophyte infection, mostly at a depth of 0-25 mm.