The efficacy of 3,4-dimethylpyrazole phosphate on N2O emissions is linked to niche differentiation of ammonia oxidizing archaea and bacteria across four arable soils

The nitrification inhibitor, 3,4-dimethylpyrazole phosphate (DMPP), can be used to reduce N2O emissions from agricultural ecosystems. However, the effectiveness of DMPP varies among soils, and this is due to both abiotic (e.g. soil properties) and biotic factors (e.g. ammonia oxidizers and denitrifier communities). Understanding the nature of these effects is necessary to improve the efficacy of DMPP, therefore encouraging wider adoption and environmental benefits. In particular, soil microbial properties associated with variation in efficacy remain largely unknown. In this study four contrasting arable soils (a grey desert soil, an alluvial paddy soil, a loess formed paddy soil, and a red soil), were characterized based on DMPP inhibition of N2O emissions and associated microbial functional guilds. DMPP significantly inhibited nitrification and N2O emissions, with an average inhibitory rate ranging from 41.7% in a red soil to 90.0% in a grey desert soil. Ammonia oxidizing bacteria (AOB) and archaea (AOA) exhibited contrasting response patterns to DMPP addition. Notably, suppression of N2O emissions by DMPP only occurred alongside fluctuations in AOB abundance. However, when AOB were inhibited, AOA abundance increased. Soil-dependent response patterns to DMPP were observed for ammonia oxidizers and denitrifiers in terms of community structure. Partial least squares path modeling (PLS-PM) found that abiotic factors, particularly pH, and biological factors such as ammonia oxidizer communities, were closely linked to N2O emissions. Our findings provide evidence that: (i) DMPP effectively inhibits nitrification through inhibiting the abundance of AOB across soil types; (ii) releasing AOA from the competition with AOB allows AOA to efficiently grow and multiply, even under high ammonium conditions; and (iii) abiotic factors play a more important role than biotic factors in soil N2O emissions.