Nitrapyrin coupled with organic amendment mitigates N2O emissions by inhibiting different ammonia oxidizers in alkaline and acidic soils

The aim of this study was to investigate the combined effects of organic manure and nitrification inhibitor on nitrogen (N) transformation, nitrous oxide (N2O) emissions and the gene abundance of ammonia oxidizers in acidic and alkaline soils. Therefore, an incubation experiment was conducted with red (pH 5.51) and calcareous soils (pH 8.12) collected from Hunan Province and Xinjiang Autonomous Region of China, respectively, including four different treatments as follows: CK (no fertilizer), U (only urea), UM (60% urea-N plus cattle manure-N), UMCP (UM + nitrapyrin). The results showed that UMCP treatment significantly increased retention time of ammonium nitrogen (NH4+-N) in both red and calcareous soils (P < 0.05), compared with the treatments of CK, U and UM. The inhibitory efficiency of nitrapyrin, based on the ratio of NH4+-N/NO3-N, was nearly twice higher in calcareous soil (71 days) than that in red soil (36 days). The potential nitrification rates (PNR) were significantly increased by the urea or urea plus manure application, but were greatly reduced by nitrapyrin addition. Nitrapyrin addition significantly inhibited the gene abundance of ammonia-oxidizing bacteria (AOB) in calcareous soil, whereas inhibited the ammonia-oxidizing archaea (AOA) growth in red soil. UMCP treatment lowered N2O emissions and increased N recovery compared with UM. Linear regression analysis showed that PNR was positively correlated with AOB (P = 0.048) and AOA abundance (P = 0.0014) in red soil, but only correlated with AOB (P = 0.0032) in calcareous soil. Random forest and structural equation model (SEM) analyses revealed that pH, NH4+-N and organic carbon (SOC) were the key factors affecting the abundance of AOA and AOB, and AOA contributes more to N2O emissions than AOB from red soil, whilst only AOB is highly responsible for the N2O production from calcareous soil. Our result suggests that nitrapyrin plus organic amendment could be serving as an effective fertilization scenario on mitigating N2O emissions and enhancing N recovery and utilization in acidic and alkaline soils.