Soil enzyme activity and stoichiometry in forest ecosystems along the North-South Transect in eastern China (NSTEC)

Soil enzymes, as indicators of microbial metabolism, play an important role in nutrient biogeochemistry at the ecosystem level. In this study, we present information from a comprehensive analysis of the latitudinal variations in, and stoichiometric relationships between, soil β-glucosidase (BG), N-acetylglucosaminidase (NAG), leucine aminopeptidase (LAP), and acid phosphatase (AP) in nine forest ecosystems along the North-South Transect in eastern China. The results showed that soil BG and NAG activities were higher in temperate forests than in subtropical and tropical forests. Soil AP activities were the opposite, which indicates that microbial nutrient demand in tropical forests was limited by the nutrient phosphorus (P). Soil BG and NAG activities were significantly and negatively correlated with mean annual temperature (MAT), mean annual precipitation (MAP), the soil carbon (C):P and soil nitrogen (N):P ratios, but not with the soil C:N ratio. Soil NAG and AP activities were inversely correlated with soil pH, and soil AP activity increased as soil pH decreased. The latitudinal variations in the C:N, C:P, and N:P acquisition ratios represented by ln(BG):ln(LAP + NAG):ln(AP) activities across ecosystems were significantly and negatively related to MAP and MAT. The C:P and N:P acquisition ratios were positively related to soil pH but negatively related to the soil C:P and N:P ratios. The C:N and C:P acquisition ratios were also negatively correlated with leaf C:N, C:P, and N:P ratios. This study provides useful information about environmental controls on enzyme stoichiometry, and also highlights the stoichiometric and energy limitations on the metabolism of soil microbes.