Nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) reducesN2Oemissions by altering the soil microbial community in a wheat-maize rotation on the North China Plain

Nitrous oxide (N2O) is a potent greenhouse gas that is released from agricultural ecosystems where nitrogen fertilizers are poorly used and contributes to global climate warming. Large nitrogen fertilizer inputs in summer maize fields on the North China Plain (NCP) lead to large N2O emissions. N2O emissions can be mitigated using 3,4-dimethylpyrazole phosphate (DMPP), but the efficiency and microbial mechanisms of this mitigation at different nitrogen rates remain poorly understood. To evaluate the efficiency of N2O emission mitigation by DMPP at different nitrogen rates and to explore its mechanisms at the microbial level, we monitored the dynamic changes in mineral and N2O fluxes and analysed the abundance and community structure of ammonia oxidizers. We found that DMPP significantly inhibited the oxidation of ammonium (NH4+) to nitrate (NO3-) and thus maintained NH(4)(+)concentrations but decreased the peak value of NO(3)(-)concentrations. Total N2O emissions were increased by 6.5-fold, 13.2-fold and 26.7-fold in fields with 112.5 kg N ha(-1), 225 kg N ha(-1)and 337.5 kg N ha(-1), respectively, compared with fields with no nitrogen applied. Nitrogen increased the abundance of ammonia-oxidizing bacteria (AOB) and decreased that of ammonia-oxidizing archaea (AOA), whereas DMPP exhibited the opposite effects. Therefore, AOB could be the dominant N2O emission contributors in nitrogen-treated soils. Sequencing results suggested that all AOB belong to theNitrosospiraandNitrosomonas nitrosagroups, and all AOA fell within theNitrososphaeragroup. In both AOB and AOA communities, changes in the second-largest cluster after the application of nitrogen fertilizer and DMPP were more pronounced than those in the largest cluster. The potential functional clusters of AOB and AOA wereNitrosospiracluster 3b andNitrososphaeracluster 4.1, respectively. This study showed that nitrogen and DMPP both affected the abundance and structure of ammonia-oxidizer communities, which may contribute to the variations in N2O emissions from croplands. Highlights Role of soil microorganisms in the efficiency of DMPP to reduce N2O emissions under different N inputs was explored. N input increased N2O emissions and DMPP reduced N2O emissions N and DMPP affect N2O emission via a changed key cluster of ammonia oxidizers. DMPP was more efficient at higher nitrogen input levels.