Response of soil extracellular enzymes to global changes: A review.

Soil extracellular enzymes (EES) regulate the formation of substrates available to soil microbes and nutrient release by catalyzing the degradation of complex macromolecules in organic matter. Therefore, EES are the key catalysts in the microbial-mediated biogeochemical cycling, playing an important role in regulating ecosystem functions. We reviewed the research advances in the formation, sources, classification, and functions of EES, ela-borated on their responses and feedback mechanisms to global changes (including climate change and human activities). Soil extracellular enzymes exhibit nonlinear responses to multiple climate factors, such as temperature rise, drought, nitrogen deposition, changes in precipitation, and increased CO2 concentration. This nonlinearity is not the result of the superposition of a single factor, but mainly stems from the interaction between climate and environmental factors. By altering the nutrient limitation status, life history strategy, and community structure of soil microorganisms, it triggers changes in enzyme activities and ecological stoichiometry. The final response depends on the intensity, duration, and environmental background of each factor. Future research should shift from single enzyme activity measurement to coupled analysis of enzyme kinetics, microbial resource allocation, and ecosystem processes. By combining long-term field experiments, isotope tracing, and multiomics techniques, further works would enhance our understanding of the multifactor interaction mechanisms under global change. Key enzyme functional parameters should be incorporated into the ecosystem model to accurately predict soil carbon dynamics and ecosystem functions under climate change.