Long-term N addition leads to microbial C, but not N limitation of poplar plantation soils in eastern China

Soil extracellular enzymes are vital to regulating soil carbon (C) and nutrient cycling, and hence affecting soil function. However, how soil enzymes activity will respond to increasing global nitrogen (N) deposition, remains poorly understood. In this study, we applied five N addition treatments (0, 5, 10, 15, and 30 g m 2 yr 1) at a coastal China poplar plantation to explore the activity of the five soil enzymes associated with C, N, and phosphorus (P) cycling and nutrient limitation of soil microbes from 2018 to 2020. We found that N addition significantly increased C, decreased N and showed no significant impact on P acquisition enzyme activity. We also found that N addition aggravated soil microbial C limitation but did not significantly change the N limitation. Both soil microbial C and N limitation were eased with time (year). Best subset regression analysis (BSS) showed that dissolved organic C, soil pH, and microbial biomass C were the dominant drivers of C, N, and P acquisition enzyme activity, respectively. Also, BSS showed that soil available N explained the greatest proportion of variation in positive soil microbial C and negative N limitation. Our study provides evidence for changes in soil enzymes activity and microbial nutrients limitation, as well as contributes to the theoretical basis for soil microbial nutrient cycling with elevated N deposition.