Net nitrification rate and ammonia oxidizer control during nutrient addition and nutrient cessation
The optimal SEM models implied by our data supported relationships among soil biogeochemical variables and AOB abundance and nitrification (Fig. 5). Specifically, N addition directly explained 75% of the AOB abundance variance. This model revealed that soil N availability was the best metric for AOB abundance changes; the decreased soil pH resulting from N additions was the second optimal predictor of AOB abundance (Fig. 5a). Increased soil microbial N directly stimulated N mineralization after N addition ceased, associated with increased AOB abundance (Fig. 5b). Also, N-induced change in the AOB community was related to high AOB abundance. Consequently, enhanced AOB abundance and MBN lead to high nitrification (Fig. 5b).