Mechanisms Of Microbial Regulations Of Forest Soil Carbon Change In Baotianman

Soil carbon sequestration in forest ecosystems is a highly complex process because of the interactive effects of vegetation, soil, microbial community, and climate. This study focus on the soil carbon transformation and turnover processes and the controlling mechanisms of microbial community in a typical forest ecosystem of the subtropical-temperate transitional zone. 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, respectively. The objectives of the study are to determine and elucidate (1) the controls of environmental factors and microbial community structure on soil organic carbon transformation and turnover;(2) variations of microenvironment, microbial community biomass, microbial community structure and functions among contrasting forest types and stand developmental stages; and (3) responses of microenvironment, soil microbial community biomass, structure and function to changes in plant carbon inputs. By addressing the abovementioned issues, this study aims to elucidate the operating mechanisms of the interactive controls of vegetation and soil microbial communities on soil carbon transformation or turnover.Major findings are as follows:1. Soil microbial community composition was strongly influenced by soil water content, soil temperature, soil carbon content, fine root mass, clay content, and C/N ratio in soils; the six biotic and abiotic factors jointly explained54%of variations in the microbial community structure.2. The Gram-negative bacteria, saprophytic fungi, and arbuscular mycorrhizal fungi community occurred as the most dominant controls on soil enzymes involved in soil carbon transformation or turnover; the three soil microbial types jointly explained65%of variations in the specific activities of five soil enzymes (i.e. β-1,4-glucosidase, cellobiohydrolase, β-1,4-N-acetylglucosaminidase, phenol oxidase, and peroxidase) assessed. Bacterial communities are strongly linked with the extracellular enzymes involved in carbon transformation; whereas saprophytic fungi are associated with activities of extracellular enzymes driving soil carbon oxidation. These findings demonstrated the complex interactions and linkage among plant traits, microenvironment, and soil physiochemical properties in directly and positively affecting soil carbon transformation and turnover via microbial regulations.3. The measured environmental factors, soil microbial biomass carbon, soil microbial biomass nitrogen, community structure, and specific activities of soil extracellular enzymes varied significantly among forest types, but not across stand age classes except soil microbial biomass carbon and soil water content; the specific activities of soil extracellular enzymes were not strongly associated with specific microbial community types.4. Soil microbial community biomass, microbial community composition and soil enzyme activity differed in responses to changes in carbon input. The effects of root trenching on soil microbial biomass carbon and nitrogen, microbial community composition and soil enzyme activity were stronger than that of litter removal or litter doubling. There were also differences in the responses of microbial biomass, community structure and soil enzyme activities to plant carbon input in an age sequence of Q. aliena forest. In addition, all the three treatments had no significant influence on soil moisture and soil temperature.