This study focuses on the controlling mechanisms of soil microbial community structure and function to the change of below-ground carbon inputs through root-trenching experiments in a typical forest ecosystem of the subtropical and temperate transitional zone in China. By combining field investigations and manipulation experiments,phospholipid fatty acids (PLFAs) and activities of soil extracellular enzymes were studied as indicators of soil microbial community structure and functioning. We also studied the response characteristics of soil microbial biomass,community structure and activities in below-ground carbon inputs. The results showed that soil microbial biomass carbon in root-trenching plots reduced significantly in an age sequence of Quercus aliena forest (40-year-old,80-year-old,and >160-year-old). Integrated over the entire experimental period; the mean difference of soil microbial biomass carbon in root-trenching plots were reduced between -8.72% and -5.72%,and the highest reduction was in the 80-year-old forests,whereas the lowest decline was in the 160-year-old forests. The variation of soil microbial biomass nitrogen was similar with the changes of soil microbial biomass carbon in the forest stands of similar age,but compared with the control plots,it did not decrease significantly. In addition,compared with the control plots,the soil microbial biomass carbon and nitrogen in all forest stands increased after trench for 2 to 4 m. The root-trenching can produce different effects on soil microbial community structure in all forest stands,the response of microbial communities to the change of below-ground carbon input in 40-year-old forests were higher than the other two age groups. The relative abundances of saprotrophic fungal community in root-trenching plots was declined sharply in all stands,and it reduced significantly in 80 and 160-year-old forests compared to control. Other communities like bacteria,actinomycete and arbuscular mycorrhizal fungi changed slightly in all forest stands; the hydrolase activities (i.e. beta-1, 4-glucosidase and beta-1, 4-N-acetylglucosaminidase) in root-trenching plots decreased remarkably in the 40,80 and 160-year-old stands,but the oxidase activity (i.e. phenol oxidase and peroxidase) was not diminish in all plots except 160-year-old stands. The root-trenching treatment had no obvious influence on soil moisture and soil temperature. By addressing the response characteristics of soil microbial biomass,community structure and function on the plant root carbon input,this study sheds light on the trends of soil microbial structure and function change under the context of global climate change. This study shows the need for more accurate prediction trends of forest soil carbon in the future.