The soil microbial biomass,the living fraction of organic matter,contains energy material organic carbon compounds,which is derived from plant residue generated soil organic matter.This study investigated the relationships between microbial biomass C and organic C with environmental parameters.The results indicate that soil microbial biomass is highly sensitive to the changes of environmental conditions in soils,and converts easily to available organic C compounds,and acts as source and sink of energy material C flow.Therefore,it plays an important role in soil organic matter decomposition.The turnover of soil microbial biomass is an important pathway of soil organic matter decomposition.