How repeated use of urease and nitrification inhibitors affect soil microbes and N2O emissions in North China Plain?

A common approach to reduce N loss is inclusion of inhibitors with the fertilizer formulation. However, the performance of commercially available inhibitors is often highly unpredictable, with efficacies lasting for few weeks or even only days, for reasons that are still poorly understood. Furthermore, how repeated use of these inhibitors affect soil microbes and nitrogen (N) transformation remains elusive. In the current study, we investigated the response of the community compositions of critical N-cycling biomarkers involved in nitrification and denitrification (including amoA, nxrA, nxrB, narG, nosZ), potential nitrification rates (PNR) and N₂O emissions to repeated addition of urease and nitrification inhibitors (nBPT, DMPP) based on a 4-year field experiment. The results demonstrated that 4 years of fertilization significantly affected the community structure of nitrifiers, except AOA. Repeated addition of inhibitors significantly reduced N₂O emissions (P ˂ 0.05) and changed the community structure of bacterial-amoA, nxrB, narG and nosZ compared to urea application alone (P ˂ 0.05), but the effects of DMPP and nBPT on N₂O emissions and soil microbes were different. Inhibitors had no significant effect on the soil PNR and archaeral-amoA and nxrA. Based on structural equation modeling, amendment with the inhibitors reduced N₂O emissions through directly affecting NH₄⁺-N substrate availability for soil microbes and subsequently changing community composition of AOB. These findings help to disentangle the interplay of nBPT and DMPP with soil microbes and N₂O emissions in North China Plain.