Quantifying the influence of 3,4-dimethylpyrazole phosphate on soil nitrous oxide production in multi-year reclaimed water-irrigated soil

3,4-Dimethyl pyrazole phosphate (DMPP) is commonly used to regulate soil nitrogen transformation and mitigate nitrous oxide (N₂O) emissions, while reclaimed water (RW) irrigation alleviates freshwater shortages but may alter soil properties, affecting N₂O emissions. However, the interaction between DMPP and RW irrigation on N₂O emission pathways remains underexplored. This study conducted a field experiment with two water quality regimes (RW and groundwater (GW)) and two nitrogen fertilizer conditions (with and without DMPP) to assess soil N₂O, nitric oxide (NO), and ammonia (NH₃) emissions. Using the ¹ ⁵N tracing technique, we investigated microbial mechanisms underlying N₂O and NO production under multi-year RW irrigation. The findings indicate that although DMPP effectively reduced soil N₂O and NO concentrations within the 0–30 cm depth, thereby lowering their emissions under RW irrigation, its application also led to an increase in soil NH₃ volatilization. Consequently, cumulative N₂O emissions shifted from 2020 to 2021, with reductions of 15.11 %–38.46 % under RW irrigation and 36.88 %–48.29 % under GW irrigation. However, the inhibitory effect of DMPP was weaker under RW irrigation compared to GW irrigation. This reduction was influenced by RW irrigation, which enhanced the abundance of nitrifying microbial communities and increased the contribution of heterotrophic nitrification to soil N₂O emissions, thereby mitigating the inhibitory effect of DMPP on autotrophic nitrification. Overall, it emphasized the need for optimized nitrogen management strategies under RW irrigation to maximize emission reductions while minimizing trade-offs in NH₃ volatilization and microbial-driven nitrogen transformations.