Long-Term Mineralization of Peatland Soil after Permafrost Thaw in Northmost China

Abstract

Northern Peatlands are crucial carbon (C) sinks and Climate-Sensitive Zones. However, little is known about the rate of C release from peatland soil in the permafrost region of northmost China under climate warming. This study employed laboratory incubation to determine C emission rates at different soil depths of a permafrost peatland in the Greater Khingan Mountains of China under two temperature conditions (5°C and 15°C). A three-pool carbon decomposition model was also used to investigate the size and turnover time of C pools in different soil layers. The results revealed that temperature significantly influences carbon dioxide CO2 emission rates, with emissions at 15°C being approximately double those at 5°C. Furthermore, even after more than 700 days of incubation, C emission peaks could still be observed, indicating the roles of carbon pools in different durations. The proportion of fast C pools in different layers was all less than 5%. As the depth increases, the proportion of the slow C pools decreases while the proportion of the passive carbon pool increases, which suggested that the stability of soil organic C (SOC) was higher in the permafrost soil than those in the active layer and the transition layer. The mean residence times of fast C pools and slow C pools at 15°C was half that at 5°C indicates a high sensitivity of peatland organic carbon to climate warming. These results indicate that warming can significantly increase the emission rate and turnover time of soil carbon in the permafrost peatland. Due to the varying decomposition rates and durations of different soil carbon pools to temperature increases, assessing the carbon emission processes in permafrost peatlands requires long-term observations and a focus on the decomposition of the slow and passive carbon pools, which constitute the majority of the total carbon pool in peatland soil.

Keywords: Carbon decomposition, peatland, CO2 emission rate, permafrost