Abiotic processes dominate short-term carbon emissions in sandy soils following rewetting

Microbial respiration is conventionally considered the primary driver of short-term carbon dioxide pulses following soil drying-rewetting cycles. However, rapid emission kinetics and delayed microbial recovery in drought-impacted soils suggest substantial abiotic contributions to carbon mineralization, particularly in arid sandy soils. Here, we quantified abiotic carbon emissions during soil drying–rewetting through microbial growth monitoring and sterilization. In sandy soils, abiotic processes dominated initial emissions, accounting for 95.5% of total carbon dioxide production within three hours after rewetting, compared to 39.5% in paddy soils. Solid-liquid interfacial reactions during rewetting drove iron and manganese redox cycling, generating reactive oxygen species that directly promoted carbon mineralization. These reactive oxygen species synergized with enzymes to degrade organic carbon, preferentially targeting dissolved organic matter with low hydrogen-to-carbon ratios and high double bond equivalents, which are typically resistant to microbial degradation. Our findings show that abiotic processes dominate short-term carbon dynamics during rewetting of arid sandy soils. Within three hours after sandy soil rewetting, redox reactions mediated by iron and manganese, combined with the generation of reactive oxygen species, induce substantial abiotic release of carbon dioxide, representing 95.5% of total emissions via direct and indirect mechanisms.