Soil enzyme activities increase following restoration of degraded subtropical forests

Ecological restoration increases biodiversity and carbon and nitrogen accumulation. Although soil enzyme activities are critical to element cycling and plant diversity and productivity in natural habitats, little is known regarding the effects of ecological restoration on the activities of soil resident enzymes. We investigated the influence of ecosystem restoration on microbial carbon and nitrogen dynamics in soil, as well as the functionality of five enzymes (catalase, dehydrogenase, polyphenol oxidase, urease, and invertase) via the extraction of samples from stands that were subjected to continuous anthropogenic disturbances (i.e., recurring fuelwood collection and domestic animal grazing) in contrast to samples obtained from stands which were left undisturbed for 6, 11, 21, and 31 years in the subtropical forests of China. We found that soil microbial biomass carbon and nitrogen increased with time since restoration, and the activities of catalase, dehydrogenase, invertase, urease, and polyphenol oxidase were amplified in the undisturbed stands following 11 years of restoration, which continued at high levels or decreased thereafter. Redundancy analysis revealed that enzyme activities were augmented in response to biomass inputs from aboveground litterfall and fine root mortality and were positively related to soil carbon and available nitrogen, phosphorus, and potassium contents. Our results highlight the multiple links between increased aboveground and belowground inputs, the abundance of soil-dwelling microorganisms and their enzyme activities, and their contributions to soil carbon and nutrient cycling following the ecological restoration of degraded subtropical forests.