The contrasting effects of N-(n-butyl) thiophosphoric triamide (NBPT) on N2O emissions in arable soils differing in pH are underlain by complex microbial mechanisms

Abstract

The urease inhibitor, N-(n-butyl) thiophosphoric triamide (NBPT), has been proposed to reduce synthetic fertilizer-N losses, including nitrous oxide (N2O) emissions from agricultural soils. However, the response of N2O emission to NBPT amendment is inconsistent across soils and associated microbial mechanisms remain largely unknown. Here we performed a meta-analysis of the effects of NBPT on N2O emissions and found NBPT significantly reduced N2O emissions in alkaline soils whereas no obvious effects exhibited in acid soils. Based on the finding of meta-analysis that pH was a key modifier in regulating the effect of NBPT on N2O emissions, we selected two arable soils differing in pH and conducted a microcosm study. In conjunction with measurement of N2O emission, community structure and abundance of functional guilds were assessed using T-RFLP and qPCR. Our results showed NBPT retarded urea hydrolysis and inhibited nitrification, but stimulated N2O emission in alkaline soil, whereas it exhibited no remarkable effects in acid soil, thereby only partly confirming the results of meta-analysis. Abundances of AOB and ureC-containing bacteria decreased, while abundance of AOA increased in both soils with NBPT addition. For acid soil, N2O emissions were significantly correlated with both abundances and community structures of AOA and ureC-containing bacteria, as well as abundance of AOB; for alkaline soil, abundances and community structures of AOB were correlated with N2O emission, as well as community structures of ureC-containing bacteria and archaea, indicating an inconsistent response pattern of community traits of N2O emissions-related functional guilds to NBPT between alkaline soil and acid soil. Our findings suggest that (i) efficacy of NBPT in N2O emission was mainly influenced by soil pH and (ii) variable effects of NBPT on N2O emission might originate not only from the direct effect of NBPT on community traits of urease-positive microbes, but from the indirect effect on ammonia oxidizers.