Abstract: Wetlands store one third of global soil organic carbon (SOC) and are strongly affected by artificial drainage. The impact of drainage-induced water-table decline on carbon cycling in different wetlands, particularly microbial transformation processes, remains unclear. To address this knowledge gap, we collected soil samples from two typical wetlands of China (a nutrient-poor bog located in Dajiuhu and a nutrient-rich fen in Hongyuan) and conducted an incubation experiment with the addition of ¹³C-labeled glucose to analyze the effects of short- and long-term drainage on SOC decomposition, extracellular enzyme activity, microbial carbon use efficiency (CUE), and microbial carbon accumulation efficiency (CAE). The results showed that both short- and long-term drainage significantly increased SOC decomposition rates in both wetlands (from 1.47 μg C·g^-1·h^-1 in submerged soils to 2.47 μg C·g^-1·h^-1 in drained soils), microbial biomass carbon derived from glucose (from 0.21 mg C·g^-1 to 1.00 mg C·g^-1) and CAE (from 0.29 to 0.73), but did not alter CUE (ranging from 0.34 to 0.86). Long-term drainage increased α-glucosidase activity in the Dajiuhu wetland and decreased β-glucosidase and phenol oxidase activities in the Hongyuan wetland. In conclusion, drainage enhanced the ‘microbial carbon pump' and its efficiency in wetlands mainly via increasing microbial intracellular metabolism (including respiration), but also acce-lerated SOC decomposition.

Key words: microbial carbon use efficiency, microbial carbon accumulation efficiency, soil organic carbon cycling, wetland, drainage