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. Endophyte infection has been shown to increase aboveground biomass production, reduce herbivory, and slow litter decomposition rates. All of which may lead to the enhancement of soil organic carbon pools in endophtye-infected (E+) versus endophyte-free (E-) tall fescue stands as has been observed in Georgia. The presence of fungal-produced mammalian and insect-toxic alkaloids is often invoked as the mechanism by which these physiologic, community, and ecosystem effects are created. Coupling a site-specific litter decomposition study with a regional soil organic carbon sampling scheme, we sought to test: 1) whether endophyte-produced alkaloids are indeed responsible for reductions in tall fescue litter decomposition rates; and 2) the generality of the endophyte soil carbon pool enhancement result from Georgia. For objective 1, we incubated E+ and E- litterbags on the soil surface in both E+ and E- tall fescue pasture located in Lexington, KY and measured mass loss and concentrations of alkaloids (ergovaline and loline) and carbon and nitrogen over a 168 day period.
Results/Conclusions:
Alkaloid concentrations in decomposing E+ litter declined over time but were still present in significantly higher concentrations in E+ vs. E- material for more than 21 days in the field. Correspondingly, 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). For our second objective, we identified and sampled soil (0-10 cm depth) from paired, adjacent E+ and E- tall fescue pastures at 9 locations throughout the southeastern U.S. Carbon content was determined on an elemental analyzer. Consistent with previous results, soil organic carbon pools were significantly greater in E+ versus E- tall fescue pastures across all sites (2889 vs. 2724 g C m-2, respectively, p=0.0098), with no significant site by endophyte interaction term. These data demonstrate that fungal endophytes, through the production of alkaloid compounds, have significant, regional ecosystem-level impacts in tall fescue pasture.
