Redox-Driven Carbon Loss in Black Soils Under Climate Warming: The Overlooked Role of Anaerobic Legacy Effects

Wetlands represent critical yet vulnerable carbon reservoirs, whose stability is threatened by increasing redox fluctuations driven by climate change and human activities. Here, we investigated the mechanisms controlling soil organic carbon (SOC) mineralization during anaerobic-aerobic transitions and under warming conditions, using three black soils from Northeast China with contrasting land-use histories. Our results showed that anaerobic CO₂ emissions increased by 29% - 44% under warming and governed by synergistic iron-organic carbon-microbe interactions, inducing the destabilization of iron-bound organic carbon. Upon oxygenation, short-term aerobic CO2 pulses were primarily driven by anaerobic legacy effects (e.g., preserved enzymes and reductants-derived •OH) rather than renewed microbial respiration, being more vulnerable to warming (25% - 31%) than prolonged oxygenation (10% - 17%) in soil A and soil B. Sterilization experiments showed that preserved enzymes contributed substantially more to aerobic CO₂ pulses (52%) than •OH-mediated oxidation (27%) in soil A. A random forest model identified •OH and anoxic hydrolases as key predictors of short-term aerobic CO₂ release (56.6% explained variance). Mechanistically, •OH played a dual role: promoting oxidative activity while simultaneously inhibiting anaerobic hydrolases. These findings establish that SOC mineralization potential and its temperature response are fundamentally determined by intrinsic soil properties, and anaerobic processes, traditionally viewed as C stabilization, may paradoxically drive C loss during redox fluctuations that intensify under climate warming.