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

Abstract

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. Under 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$_{2}$