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

Abstract

Empirical evidence of the contemporaneous variations in soil organic carbon (SOC) fractions, C-cycling associated hydrolytic enzyme activities, and microbial carbon metabolism during the development of plantations has not been satisfactorily documented. Microbial activity and extracellular enzymes play a crucial role in driving biogeochemical processes, yet the mechanisms by which biotic and abiotic factors interact influence SOC fractions remain unclear. In this study, we evaluated the changes in the SOC, microbial biomass carbon (MBC), easily oxidizable 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 SOC fractions, three enzyme activities, and microbial carbon metabolism decreased from 6a to 12a, 18, or 25a, and then increased in 32a and 49a, but the DOC at the 0–20 cm and 20–40 cm soil depths generally increased with stand age across all six stand ages. The SOC fractions, enzyme activities, and microbial activities were higher in both May and September than in January. The concentrations of SOC, MBC, EOC, DOC were positively correlated with the activities of three enzymes and the microbial Shannon diversity. Altogether these findings indicate that microorganisms and extracellular enzymes are sensitive to SOC dynamics with stand age and that to understand SOC dynamics, we need to consider the multiple factors of forest ecosystems.