Soil organic carbon fractions C-cycling associated hydrolytic enzymes and microbial carbon metabolism vary with stand age in Cunninghamia lanceolate (Lamb.) Hook plant

Empirical evidence of the contemporaneous variations in soil organic carbon (SOC) fractions, C-cycling associatedhydrolytic enzyme activities, and microbial carbon metabolism during the development of plantations hasnot been satisfactorily documented. Microbial activity and extracellular enzymes play a crucial role in drivingbiogeochemical processes, yet the mechanisms by which biotic and abiotic factors interact influence SOC fractionsremain unclear. In this study, we evaluated the changes in the SOC, microbial biomass carbon (MBC), easilyoxidizable carbon (EOC), and dissolved organic carbon (DOC), the invertase, cellulase, and β-glucosidase activities,and microbial carbon metabolism activities at the soil depths of 0–20 cm, 20–40 cm, and 40–60 cm in 6-(6a), 12- (12a), 18- (18a), 25- (25a), 32- (32a), and 49-year-old (49a) Chinese fir plantations. Overall, the SOCfractions, three enzyme activities, and microbial carbon metabolism decreased from 6a to 12a, 18, or 25a, andthen increased in 32a and 49a, but the DOC at the 0–20 cm and 20–40 cm soil depths generally increased withstand age across all six stand ages. The SOC fractions, enzyme activities, and microbial activities were higher inboth May and September than in January. The concentrations of SOC, MBC, EOC, DOC were positively correlatedwith the activities of three enzymes and the microbial Shannon diversity. Altogether these findings indicate thatmicroorganisms and extracellular enzymes are sensitive to SOC dynamics with stand age and that to understandSOC dynamics, we need to consider the multiple factors of forest ecosystems.