Mineral–Enzyme Interactions Drive Soil Organic Carbon Accumulation and Stabilization in Permafrost

Constraining the stability and bioavailability of soil organic carbon (SOC) in permafrost regions is crucial to predicting future greenhouse gas emissions under global warming and permafrost thawing. Oxidative enzymes like peroxidases, often stabilized by minerals, play critical roles in degrading recalcitrant organic matter, yet their contribution to SOC persistence in soils from permafrost regions remains unexplored. Here, using amino sugar biomarkers, we assessed how peroxidase activity and minerals influence microbially processed SOC across two contrasting permafrost types: high-altitude Tibetan Plateau grasslands (warm permafrost) and high-latitude Alaskan tundra (cold permafrost). Tibetan soils contained 4-fold higher microbial residue-derived SOC than Alaskan soils, with fungal necromass three times higher than bacterial necromass, while fungal necromass in Alaskan soils exceeded bacterial necromass by an order of magnitude. In both regions, strong association of SOC and microbial necromass with short-range ordered minerals underscores the role of mineral-microbe interactions in SOC stabilization. Strikingly, peroxidase activity in Alaskan soils was 1 order of magnitude higher than in Tibetan soils and was tightly correlated with mineral-bound organic carbon. These findings suggest that peroxidase-driven H₂O₂ reduction represents a previously unrecognized mechanism of SOC stabilization in Arctic permafrost, with important implications for carbon-climate feedbacks under warming.