Rhizosheaths stimulate short-term root decomposition in a semiarid grassland.

Rhizosheaths are frequently found in arid and semiarid ecosystems, but their impacts on root decomposition rates and associated carbon (C) and nutrient fluxes remain unclear. We investigated mass, C and nitrogen (N) loss for the roots of Stipa krylovii and Carex korshinskii; the roots were exposed to rhizosheaths, bulk soil, or no soil in litterbags during a 102-d short-term decomposition experiment. Compared with no soil addition, rhizosheath addition increased the mass loss by 39% for S. krylovii, a sheath-forming grass, and by 11% for C. korshinskii, a non-sheath-forming grass. Rhizosheath addition also increased root C loss by 39% and N loss by 41% for S. krylovii but did not significantly alter root C or N loss for C. korshinskii, which may be due to a "home-field advantage" effect. In contrast, bulk soil addition did not alter mass, C, or N loss for either plant species, possibly because bulk soils contained fewer nutrients (C, N, and phosphorus) than rhizosheaths. We demonstrate for the first time that conventional root decomposition studies that do not account for rhizosheaths will underestimate the root mass, C and N loss by >20% in semiarid grasslands. Future studies should emphasize the crucial yet unappreciated role of rhizosheaths in driving soil organic matter cycling.