The regulatory mechanism controlling nitrification inhibitors-induced mitigation of nitrification and NO-N leaching in alkaline purple soil.

Nitrification inhibitors (NIs) are critical to reduce nitrogen (N) leaching losses. However, the efficacy of different NIs can be highly variable across soils and crop types, and a deeper understanding of the mechanistic basis of this efficiency variation, especially in purple soil under vegetable production, is lacking. To enrich this knowledge gap, the impact of different NIs amendment (3,4-dimethylpyrazole phosphate, DMPP; dicyandiamide, DCD; nitrapyrin, NP) on nitrification and the microbial mechanistic basis of controlling nitrate (NO-N) leaching of vegetable purple soil was explored in southwest China. The results showed that DCD and NP effect is dose-dependent, with 10% DCD, 1% DMPP and 1% NP were found to be optimal for nitrification inhibition in vegetable purple soil. When compared with the control treatment without NIs amendments, DCD, DMPP and NP reduced NO-N leaching by 26.3%, 30.6% and 19.2%, respectively. It was noteworthy that NO-N leaching inhibition was mediated predominantly by inhibiting ammonia-oxidizing bacteria (AOB) abundance. DCD, NP and DMPP incorporation decreased the AOB abundance by 39.8%, 73.2% and 51.4% and suppressed the ammonia monooxygenase (AMO) activity by 22.2%, 36.8% and 28.7%, respectively, in comparison with the control treatment without NIs amendments. DMPP inhibited AOB abundance and AMO activity much more than DCD and NP. DMPP also significantly decreased AOB alpha diversity and altered their community structure, whereas DCD and NP had no significant effect. The mantel test indicated that AOB abundance and AMO activity are strongly correlated with NO-N leaching rate. These results show that soil application of 1% DMPP effectively mitigates NO-N leaching from sub-tropical alkaline purple vegetable soil. This study also expanded our mechanistic understanding of NO-N leaching and its regulators in an alkaline soil vegetable production system with N fertilizer and NI inputs.