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).