As soil microorganisms decompose the organic matter,they also assimilate a portion of the nutri- ent in soils to build their body.The nutrients in soil microbial biomass are mineralized from the dead mi- croorganisms.Therefore,soil microbial biomass is considered as a source and sink for nutrients,and is an active pool of organic matter in soils.Because of its important role in various ecological systems,nitrogen contained in soil microbial biomass(i.e.,SMBN) has got much attention in recent years.This ...