The 2008 Joint Meeting of the Society for Range Management and the America Forage and Grassland Council. |
Tuesday, January 29, 2008
13
Endophyte Effects on Soil Nutrient Pools, Microbial Communities, and Litter Decomposition Rates in Tall Fescue Pasture
J.A. Siegrist and R.L. McCulley. Plant and Soil Science, Univeristy of Kentucky, Ag. Science Bldg. North N-222, 1100 Nicholasville Rd, Lexington, KY 40546
Fungal endophyte symbionts of tall fescue are known to alter the physiology of individual plants, as well as affect changes in community structure and ecosystem function. Using a regional sampling approach, we sought to test the generality of prior results from Georgia that showed endophyte-infected (E+) tall fescue pastures had larger soil carbon pools and altered soil microbial communities. We sampled soil (0-10 cm depth) from paired E+ and endophyte-free (E-) tall fescue pastures at 12 locations throughout the southeastern U.S. Carbon and nitrogen content was determined on an elemental analyzer, and the phospholipid fatty acid technique assessed differences in the microbial communities. Although soil C, N, and microbial biomass tended to be greater in high- versus low-endophyte infected pastures (2.03 vs. 1.97 %C, 0.19 vs. 0.18 %N, and 16.6 vs. 13.6 nmol g-1 dry soil), the endophyte effect on these ecosystem parameters when averaged across all sites was not significant. Because enhanced soil carbon storage under E+ tall fescue is thought to result in part from the endophyte-produced alkaloids reducing decomposition rates, we also performed a litter decomposition experiment. We incubated E+ and E- litterbags on the soil surface in both E+ and E- pasture. Despite the fact that alkaloid concentrations in decomposing E+ litter decreased rapidly (89.3% loss after 21 days), E+ litterbags decomposed more slowly than E- (0.033 g day-1 vs. 0.038 g day-1 mass loss for E+ and E- litterbags after 21 days, respectively), and both types of litter decomposed more slowly when placed in E+ pasture (2.4% and 2.0% greater mass in E+ pastures for E+ and E- litterbags). These data demonstrate that fungal endophytes can have ecosystem-level impacts in tall fescue pasture; however, the strength of these impacts may be determined by site specific characteristics, such as climate, texture, and age of the stand.