Net N mineralization and nitrification rate
N mineralization rate in soil was significantly higher in R30 and R90 than in other treatments (Fig. 4). Net nitrification rate increased along the N input gradient after the N addition cessation (Fig. 4). Compared to R0, net nitrification rates increased by 20%, 39%, and 64% in R60, R90, and R120 treatments, respectively (Fig. 4). Pearson correlation analysis showed that N mineralization rates significantly positive correlated with AOB abundance (r= -0.45, p < 0.05) and microbial biomass N (r= -0.47, p < 0.05). Similarly, increased net nitrification rate was significantly related to AOB abundance (r= -0.57, p < 0.05) and microbial biomass N (r= -0.73, p < 0.001) (Fig. S2).