Background and aims <p>Anthropogenic activities induce exogenous nitrogen (N) and phosphorus (P) inputs that can affect wetland soil properties, plant biomass, and ecoenzyme activities, thereby regulating soil carbon (C) cycling. However, currently, the changes and sensitivity of soil organic C components to exogenous nutrient inputs during wetland degradation are poorly understood.</p> Methods <p>We analyzed changes in soil organic C components in non-degraded and degraded wetlands in the Songnen Plain under N, P, and N + P inputs and used analyses of variance, correlation analysis, redundancy analysis, and structural equation modeling to explore the mediating mechanisms of soil properties, plant biomass, and ecoenzyme activities on soil organic C components.</p> Results <p>Soil properties, plant biomass, ecoenzyme activities, and soil organic C components were mainly affected by N input in non-degraded wetlands and by N and P inputs in degraded wetlands. Redundancy analysis revealed that soil properties, plant biomass, and ecoenzyme activities explained 85.2%, 42.4%, and 42.8% of the variations in soil organic C components under nutrient inputs, respectively. Further, structural equation model revealed N and P inputs directly affected soil organic C components by altering soil total N, total P, and water content, or indirectly by altering plant biomass and ecoenzyme activities.</p> Conclusions <p>Wetland degradation can increase the sensitivity of soil organic C components to nutrient input. This response process is primarily driven by soil properties, although plant biomass and ecoenzyme activities also play important regulatory roles. These findings are crucial for protecting wetland soil C pools and mitigating global climate change.</p>