Changes of natural 13C abundance in microbial biomass during litter decomposition

The carbon (C) isotopic composition of soil microbial biomass (SMB) was measured in litter-amended and control plots located at three different elevations (280-2210 m, sea level) during the decomposition of plant litter (Vicia villosa) added to upland soils in southwest China. Fourteen months around the addition of litter, soil microbial biomass carbon (SMBC) was followed during experiments. Results showed that SMBC was significantly higher in the litter-amended plots than the controls at the two lowest but not the highest elevation and there was no corresponding difference in microbial δ13C values at the same time. However, microbial δ13C values at the two lowest sites were significantly higher in the litter-amended plots immediately following the peak of microbial C. The δ13C value of SMBC in litter-amended plot was higher than that in control plot, indicating that the degree of microbial decomposition and quality of plant litter will effect on shift of δ13C values of SMBC, which may be mainly caused by microbial selective utilization of organic compounds. The sequence of magnitude of δ13C value of SMBC was consistent with that of soil organic carbon (SOC) among three experiment sites, indicating that the δ13C value of SMBC reflects gross changes in the δ13C value of SOC in the corresponding samples.