Invasive Grass Alters Litter Decomposition by Influencing Macrodetritivores

The results of nitrogen (N) fertilization experiments have shown inconsistent rates of plant litter decomposition, a phenomenon that may be explained by dispropotionate influence of animal detritivores (macro-detritivores) on litter mass loss versus that of microbial decomposers, whose activity may be dependent on inorganic N. In turn, macrodetritivores may be influenced by plant species composition via their selection of optimal food resources and habitats. In our experiment, fertilizer had no apparent effect on litter decomposition, suggesting that microbial decomposers did not use the additional inorganic N and/or that macrodetritivores had a greater influence on decomposition. Manipulation of macrodetritivores suggested that plant species composition—dominated in this study by Festuca arundinacea, an exotic, invasive grass, and Aster ericoides, a native forb—caused shifts in detrivore communities and/or feeding patterns that tended to increase litter mass loss. Canopy cover of F. arundinacea and A. ericoides ranged from 0% to 11%, suggesting that low-intensity invasion may produce significant changes in ecosystem function, such as decomposition.