Fungal endophyte symbionts of tall fescue are known to alter the physiology of individual plants, as well as effect changes in community structure and ecosystem function. Using a regional sampling approach, we sought to test whether results from Georgia that showed endophyte-infected (E+) tall fescue pastures had larger soil carbon pools and altered soil microbial communities were applicable to a broader area. We sampled paired, adjacent E+ and endophyte-free (E-) tall fescue pastures at 12 locations throughout the southeastern U.S. In older pastures, soil carbon, nitrogen, and total microbial biomass were larger in E+ than E- pastures (3.46 vs. 3.26 %C, 0.31 vs. 0.28 %N, and 16.6 vs. 13.6 nmol per g dry soil for E+ and E- soils, respectively). The phospholipid fatty acid technique used to assess microbial community composition showed few differences between E+ and E- tall fescue pasture. Because enhanced soil carbon storage under E+ tall fescue is thought to result in part from endophyte-produced phenolic compounds reducing rates of litter decomposition, we complemented our regional soil-endophyte study with a local litter decomposition experiment. We incubated E+ and E- litter in bags placed on the soil surface, using a reciprocal transplant design in both E+ and E- pasture. As predicted, E+ litterbags decomposed more slowly than E-, and both types of litter decomposed more slowly when placed in E+ pasture. By measuring phenolic concentrations in the litter over time, we were able to show that indeed these endophyte-derived compounds appear to drive the differences in decomposition rates between E+ and E-litter that we observed. Fungal endophyte symbionts have significant ecosystem-scale impacts in tall fescue dominated pastures throughout the southeastern U.S.