Fertilizer stabilizers reduce nitrous oxide emissions from agricultural soil by targeting microbial nitrogen transformations

Abstract

Nitrous oxide (N2O) is a pollutant released from agriculture soils following N fertilizer application. N stabilizers, such as N-(n-butyl) thiophosphoric triamide (NBPT) and 3,4-dimethylpyrazole phosphate (DMPP) could mitigate these N2O emissions when applied with fertilizer. Here, field experiments were conducted to investigate the microbial mechanisms by which NBPT and DMPP mitigate N2O emissions following urea application. We determined dynamic N2O emissions and inorganic N concentrations for two wheat seasons and combined this with metagenomic sequencing. Application of NBPT, DMPP, and both NBPT and DMPP together with urea decreased mean N2O accumulative emissions by 77.8, 91.4 and 90.7%, respectively, compared with urea application alone, mainly via repressing the increase in NO2− concentration after N fertilization. Sequencing results indicated that urea application enriched microorganisms that were positively correlated with N2O production, whereas N stabilizers enriched microorganisms that were negatively correlated with N2O production. Furthermore, compared to urea application alone, NBPT with urea reduced the abundances of genes related to denitrification, including napA/nasA, nirS/nirK, and norBC, resulting in a higher soil NO3− pool. Conversely, DMPP application, either alone or together with NBPT, decreased the abundance of genes involved in ammonia oxidation and denitrification, including amoCAB, hao, napA/nasA, nirS/nirK, and norBC, and maintained a greater soil NH4+ pool. Both N stabilizers resulted in similar abundances of nirABD—which is related to NO2− reducers—as when no N fertilizer was applied, which could prevent NO2− accumulation, consequently mitigating N2O emissions. These findings suggest that the high effectiveness of N stabilizers on mitigating N2O emissions could be attributed to changes to soil microbial communities and N-cycling functional genes to control the by-product or intermediate products of microbial N-cycling processes in agricultural soils.