Variations in carbon-decomposition enzyme activities respond differently to land use change in central China

The turnover of soil organic carbon (SOC) is primarily regulated by extracellular enzymes secreted by the microorganism. However, how soil C-decomposition enzymes respond to different land use change remains unclear. Here, we conducted a study to explore seasonal variations in C-decomposition enzyme activities including hydrolases (alpha-glucosidase, beta-glucosidase, cellobiohydrolase, and beta-xylosidase) and oxidases (polyphenol oxidase and peroxidase) in woodland, shrubland, cropland, and adjacent uncultivated soils in central China. Soil dissolved organic C (DOC), SOC, labile C (LC), recalcitrant C (RC), soil C recalcitrance index (RIC: RC/SOC ratio), pH, soil moisture, and temperature were also investigated. Both afforested and cropland averaged higher hydrolase and oxidase activities compared with the uncultivated land, with higher levels of enzyme activities in topsoils than deep soils. By comparing with the uncultivated land, higher hydrolytic enzyme activities in afforested soils were mainly attributed to higher DOC and LC contents, whereas higher hydrolase activities in cropland soils were possibly due to lower C:nitrogen (N) ratios and agricultural disturbance (i.e., fertilization and tillage). In contrast, two oxidases activities were the highest in the cropland, which might be attributed to higher RIC and lower C:N ratio. Cropland soils also averaged higher specific enzyme activities (i.e., enzyme activities per unit of SOC) compared with the afforested land, indicating fast C turnover rates in cropland. Seasonal variations in soil enzyme activities were primarily driven by soil temperature and pH. Overall, our results reveal the different underlying mechanisms between hydrolases and oxidases in response to types of land use change.