The Degree of Permafrost Degradation Determines the Stability of Soil Organic Matter

Global warming profoundly alters the stability of soil organic matter (SOM) in permafrost zones, yet the underlying mechanisms governing SOM stability in permafrost landscapes at different stages of degradation remain unclear. This study utilised soil samples from the 0-50 cm layer collected from both continuous and isolated patches permafrost zones in the Daxing'an Mountains for laboratory incubation experiments at constant temperatures of 5 and 15 °C. The results for SOC, Fe and Al oxide content, δ ¹³C and MBC indicate that SOM in isolated patchy permafrost possesses greater bioavailability and higher decomposability under warming, and carbon mineralization in shallow soils is more temperature-sensitive (Q₁₀ = 4.24). After 89 days of incubation, the mineralisation rate in mineral-rich deep soil was only half that of organic-rich surface soil. Furthermore, as the ratio of Fe/Al oxides to organic carbon increased, the sensitivity of SOM decomposition to temperature decreased significantly. Overall, the stability of organic matter in permafrost is jointly regulated by the intrinsic molecular properties of the organic matter and the protective effect of minerals; furthermore, this protective effect can significantly delay the process by which peatlands in permafrost regions transition from carbon sinks to carbon sources.