Soil nitrogen-hydrolyzing enzyme activity and stoichiometry following a subtropical land use change

Soil extracellular enzyme activities reflect the microbial nutrient demand by microorganisms and can be strongly affected by land use change. However, how soil N-hydrolyzing enzymes and soil extracellular enzyme stoichiometry (EES) respond to land use change remains unclear. Here, we explored seasonal variations in beta-1,4-N-acetyl glucosaminidase and leucine aminopeptidase activities and EES under afforested land (woodland and shrubland), cropland, and uncultivated land for better understanding microbial metabolism around the Danjiangkou Reservoir area. Both afforested and cropland soils averaged higher N-hydrolyzing enzyme and specific enzyme activities [i.e., enzyme activities per unit of soil organic nitrogen (SON)] compared to the uncultivated soils, indicating fast N turnover rates after afforestation and cultivation. Higher N-hydrolyzing enzyme activities under afforestation and cultivation could be attributed to increasing soil organic carbon and soil organic nitrogen contents. All land use types were generally restricted by nutrients limitation than C demand as mean soil ecoenzymatic C:N:P ratios deviated from 1:1:1. However, afforestation and cultivation r|esulted in greater C demand and alleviate nutrient limitation for soil microorganisms with higher ecoenzymatic C:N ratios, C:P ratios, and vector lengths. In addition, all land use types were restricted by P than N limitation with ecoenzymatic N:P ratios less than 1 and vector angle >45 degrees, among which afforestation increased P limitation and cultivation alleviated P limitation for microbes compared with uncultivated land. Overall, our results provide insight into mechanisms of soil microbial metabolic limitation regulated by soil N-hydrolyzing enzyme activity and EES under global land use change.

Automated summary

The study found that afforestation and cultivation can increase soil N-hydrolyzing enzyme activities and accelerate nitrogen turnover rates, while soil extracellular enzyme activities are also influenced by seasonal variations. Different land use types show varying levels of sensitivity to nutrient limitation.