Long-term carbon release of peatland soil after permafrost thaw in northmost China

Northern peatlands, serving as critical carbon (C) sinks and climate-sensitive ecosystems, face uncertainties regarding their carbon release dynamics under warming conditions. This is particularly evident in the understudied permafrost regions of northern China. This study investigated soil organic carbon release across active (0–60 cm below the soil surface), transition (60–80 cm below the soil surface), and permafrost (80–160 cm below the soil surface), transition, and permafrost layer of a peatland located in the Greater Khingan Mountains of northmost China, using long-term anaerobic incubation experiments conducted at both 5 ℃ and 15 ℃. A three-pool decomposition model further quantified carbon pool sizes and turnover times. Warming significantly enhanced carbon emissions, doubling CO₂ release and increasing CH₄ emission by up to 20-fold. The active layer dominated CO₂ release whereas the transition layer exhibited peak CH₄ emissions. Carbon pool analysis revealed that the fast C pool—characterized by short mean residence time (MRT: 16–54 days)—accounted for a minor fraction (2 %−5 % of SOC) across all soil layers. Meanwhile, the slow C pool (MRT: 2–13 years) comprised about one-third of SOC. In contrast, passive C pools (MRT: millennial-scale) stored the majority of SOC (57 %−67 %). Warming reduced the mean residence time of both fast and slow C pools by 50 % in the active and transition layers. In the permafrost layer, it accelerated their turnover time by 40 %. These results indicate that prolonged warming enhanced both carbon emission rates and turnover efficiency, rendering deeper, stabilized permafrost carbon increasingly vulnerable. These findings highlight the need for long-term, multi-depth monitoring of carbon dynamics in northern peatlands to accurately predict carbon-climate feedbacks in permafrost regions.