Abstract: Soil microbial quotient,ratio of soil microbial biomass C to total organic C (MBC/SOC),is recommended as a sensitive indicator in the dynamics of topsoil organic C and soil fertility.However,whether it is applicable to subsoils derived from different parent materials is still unclear.Three soil profiles derived from different parent materials (red soil derived from granite,acidic purple soil and red soil derived from Quaternary red clay) were digged down to the soil C/R horizon,and the subsoil microbial quotient and its distribution were studied.Results showed that contents of MBC and SOC decreased with soil depth,while the microbial quotient increased in some deep subsoil horizons (illuvial or parent material horizon).Besides,content of soil dissolved organic carbon (DOC) was also increased in some deep horizons of acidic purple soil and red soil derived from granite.The increase of subsoil DOC/SOC can partially explain the profile distribution of microbial quotient.Regression analysis showed that the content of MBC was positively correlated with SOC and DOC contents,with a much higher R² for DOC.This study implied that microbial quotient could not indicate the dynamics of SOC and soil fertility in subsoil derived from different parent materials in east Hunan Province,other soil indices (e.g.,SOC and MBC) would be comprehensively considered for soil fertility evaluation.