4. DISCUSSION
N and P additions differently affected the magnitude and direction of PEs, decomposition of plant-derived substrate and SOC, microbial CUE, and thus C accumulation. This was mainly associated with the N and P additions-induced differences in soil nutrient status and microbial ecological stoichiometric ratios, as well as differences in substrate decomposability due to changes in plant community composition and plant species’ predominance. Glucose induced positive PEs while vanillin induced negative PEs. These results were in accordance with our hypotheses. However, the positive PEs with glucose amendment was mainly generated by “nutrient mining” while negative PEs with vanillin amendment was generated by the balanced two mechanisms “co-metabolism” and “nutrient mining”. This partially supported our hypotheses. The comprehensive effects on C decomposition and accumulation led to declines in SOC contents in response to N and P additions.