Enzyme Kinetics Affecting Thermal Sensitivity of SOC Decomposition Differ in Hummocks and Hollows of a Permafrost Bog

Northern peatlands are important pools of soil organic carbon (SOC) and show a fine‐scale feature of hummocks and hollows. However, there remains uncertainty about the magnitude of SOC–climate feedbacks because of the knowledge gap about the fine‐scale spatial pattern and temperature sensitivity ( Q 10 ) mechanism of SOC decomposition. We collected peatland soils from the Greater Khingan Mountains in Northeastern China to investigate how soil enzyme kinetics control the hummock–hollow pattern of the Q 10 of SOC decomposition. Results revealed that soil enzyme kinetic parameters (maximum reaction velocity [ V max ] and Michaelis constant [ K m ]) were greater in hollows compared to hummocks. In the 0–15 cm depth, the catalytic efficiencies ( K cat ) of β‐1,4‐glucosidase (BG) and acid phosphatase (AP) were greater in hollows than in hummocks, but the K cat of 4‐N‐acetylglucosaminidase (NAG) was reversed. In the 15–30 cm depth, the K cat of NAG and AP was greater in hollows than in hummocks, but the K cat of BG was reversed. Except for the K m of NAG, all enzyme kinetic parameters increased with rising temperature. The Q 10 values of V max and K m were greater in hummocks than in hollows, with Q 10 values of V max ranging from 1.48 to 2.22 and from 1.12 to 2.12 for hummocks and hollows, respectively. Similarly, the Q 10 values of K m ranged from 0.70 to 1.67 and from 0.55 to 1.50 for hummocks and hollows, respectively. A positive correlation was observed between V max and K m , indicating that increases in K m may counterbalance increases in V max as temperature rises. The Q 10 values for SOC decomposition were greater in hummocks than in hollows, with average Q 10 values of 3.5 and 1.5 when temperature increased from 5°C to 15°C, respectively. Soil TP and the Q 10 – V max of NAG and AP have emerged as the best predictors of Q 10 values for SOC decomposition, and they were positively correlated with the Q 10 values for SOC decomposition. The larger phosphorus content and the high temperature sensitivity of hydrolase activities on hummocks suggest they would have a high potential for carbon mineralisation in the background of climate warming. These findings suggest that soil enzyme kinetic parameters and their Q 10 provide valuable tools for predicting the response of microbially mediated SOC decomposition to climate warming scenarios.