Soil extracellular enzymes as drivers of soil carbon storage under nitrogen addition

Enhanced anthropogenic nitrogen (N) inputs to ecosystems may have substantial impacts on microbially mediated soil organic carbon (SOC) cycling. One way to link species-rich soil microbial communities with SOC cycling processes is via soil extracellular enzyme activities (EEAs). However, the effects of N addition on EEAs and the associated driving factors remain poorly understood. By conducting a meta-analysis, we find that N addition increases hydrolytic C-degrading EEAs that target simple polysaccharides decomposition by 12.8%, but decreases oxidative C-degrading EEAs that degrade complex phenolic macromolecules by 11.9%. The net effect of N addition on SOC storage is determined by the shifts between these two types of C-degrading EEAs, and the impacts varied across different ecosystem types. These insights highlight the crucial but understudied roles of hydrolytic and oxidative C-degrading EEAs on SOC dynamics with ongoing enhanced anthropogenic N loading. Understanding the mechanisms behind these C-degrading EEAs could help optimize SOC sequestration and inform climate mitigation strategies across different ecosystems.