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

Highlights: • NBPT was more effective in retarding urea hydrolysis in alkaline soil than in acid soil. • NBPT stimulated N₂O emission in alkaline soil but had little effect in acid soil. • NBPT decreased the abundance of AOB and ureC-containing bacteria, but increased the abundance of AOA. • The contrasting effects of NBPT on N₂O emissions in pH-different soils were 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 (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.