The contrasting effects of N-(n-butyl) thiophosphoric triamide (NBPT) on N 2 O emissions in arable soils differing in pH are underlain by complex microbial mechanisms.

The urease inhibitor, N-(n-butyl) thiophosphoric triamide (NBPT), has been proposed to reduce synthetic fertilizer-N losses, including nitrous oxide (N2 O) emissions from agricultural soils. However, the response of N2 O 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 N2 O emissions and found NBPT significantly reduced N2 O 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 N2 O emissions, we selected two arable soils differing in pH and conducted a microcosm study. In conjunction with measurement of N2 O 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 N2 O 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, N2 O 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 N2 O emission, as well as community structures of ureC-containing bacteria and archaea, indicating an inconsistent response pattern of community traits of N2 O emissions-related functional guilds to NBPT between alkaline soil and acid soil. Our findings suggest that (i) efficacy of NBPT in N2 O emission was mainly influenced by soil pH and (ii) variable effects of NBPT on N2 O 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.