Drying-rewetting events enhance the priming effect on soil organic matter mineralization by maize straw addition

Soil moisture serves as a pivotal environmental variable that governs the cycling of soil carbon (C). Although numerous studies have been conducted to evaluate the impact of drying-rewetting cycles on soil organic matter (SOM) mineralization, the dynamic changes in SOM priming effect (PE, i.e. the change in SOM mineralization after the addition of an exogenous substrate) under frequent drying-rewetting cycles remain unknown. Here, we conducted a 209-day incubation experiment utilizing 13C-labeled maize (Zea mays L.) straw to investigate how repeated drying-rewetting events influence straw decomposition, SOM mineralization, PE, and soil net sequestration of straw-C. The experimental design involved two contrasting soil moisture conditions (constant vs. varying water content) with or without maize straw amendment. Results showed that, in the absence of maize straws, drying-rewetting cycling did not significantly alter the cumulative SOM mineralization throughout the incubation period. Conversely, in the presence of maize straws, the cumulative decomposition of straws under drying-rewetting cycles was diminished by 9.8% compared to the constant water conditions. Moreover, a notable increase of the cumulative PE by 19.3% under recurrent drying-rewetting events resulted in a substantial reduction of soil net C sequestration of straw-C (straw-derived C incorporated into the soil minus the C loss primed by straw) by 22.3% compared to the constant water conditions after 209-day incubation, suggesting that frequent drying-rewetting might diminish the function of soil as a C sink. Overall, drying-rewetting cycles generally decelerated straw decomposition and reduced the recovery of straw-C in microbial biomass C and soil matrix, indicating that enhanced frequency and intensity of drying-rewetting cycles in future climate scenarios may have detrimental effects on soil C sequestration.