Hydrolase-oxidase responses mediate distinct carbon dynamics following wetland conversion to paddy versus upland systems

Extensive conversion of natural wetlands to agricultural systems threatens their carbon storage capacity. Predicting post-conversion soil organic carbon (SOC) dynamics remains challenging, largely due to poorly characterized SOC decomposition patterns across conversion pathways. Given that hydrolases target labile polymers and oxidases degrade recalcitrant polymers, their differential responses may explain divergent SOC dynamics following wetland conversion. Through a global meta-analysis (424 observations from 113 studies), we assessed enzymatic responses following conversion to paddies or uplands. We found three key patterns: (i) Conversion to paddies increased hydrolase activities by 83 % (95 % CIs: 50–123 %) while maintaining stable oxidase levels (p > 0.05), whereas conversion to uplands elevated both hydrolase [47 % (27–71 %)] and oxidase [54 % (27–88 %)] activities; (ii) Pre-conversion wetland biogeochemical properties (e.g., coastal salinity, peatland acidity) modulated enzymatic responses following conversion to uplands but not to paddies; and (iii) Conversion to uplands exhibited a rapid early-stage (0–30 years) increase in hydrolase activities, which subsequently reached a steady state. In contrast, conversion to paddies showed no discernible change in hydrolases initially, with a significant accumulation occurring only in the later period (30–150 years). Oxidase activities demonstrated a progressive increase in uplands over time but remained stable in paddies across all time periods. Critically, oxidase response negatively correlated with SOC contents, while hydrolase responses were positively linked to CO₂ emission fluxes. These relationships suggested that conversion to paddies may preserve SOC stocks despite increasing CO₂ emissions, while conversion to uplands may result in substantial SOC loss with relatively low greenhouse gas emissions. Our findings confirmed differential enzymatic responses across conversion pathways, providing enzyme-based insights for explaining post-conversion SOC dynamics in converted agricultural systems.