Effect of the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) on N-turnover, the N${}_2$O reductase-gene nosZ and N${}_2$O:N${}_2$ partitioning from agricultural soils

Nitrification inhibitors (NIs) have been shown to reduce emissions of the greenhouse gas nitrous oxide (N${}_2$O) from agricultural soils. However, their N${}_2$O reduction efficacy varies widely across different agro-ecosystems, and underlying mechanisms remain poorly understood. To investigate effects of the NI 3,4-dimethylpyrazole-phosphate (DMPP) on N-turnover from a pasture and a horticultural soil, we combined the quantification of N${}_2$ and N${}_2$O emissions with ${}^{15}$N tracing analysis and the quantification of the N${}_2$O-reductase gene (nosZ) in a soil microcosm study. Nitrogen fertilization suppressed nosZ abundance in both soils, showing that high nitrate availability and the preferential reduction of nitrate over N${}_2$O is responsible for large pulses of N${}_2$O after the fertilization of agricultural soils. DMPP attenuated this effect only in the horticultural soil, reducing nitrification while increasing nosZ abundance. DMPP reduced N${}_2$O emissions from the horticultural soil by >50% but did not affect overall N${}_2$ + N${}_2$O losses, demonstrating the shift in the N${}_2$O:N${}_2$ ratio towards N${}_2$ as a key mechanism of N${}_2$O mitigation by NIs. ... mehrUnder non-limiting NO${}_3$${}^{-}$ availability, the efficacy of NIs to mitigate N${}_2$O emissions therefore depends on their ability to reduce the suppression of the N${}_2$O reductase by high NO${}_3$${}^{-}$ concentrations in the soil, enabling complete denitrification to N${}_2$.