Responses of N2O emissions to straw addition under different tillage soils: A 15N labelling study.

Nitrous oxide (N 2 O) emissions contribute to global climate change and are regulated by the intensities of N mineralization, nitrification and denitrification processes. These processes depend on soil management, e.g., tillage and straw addition. Microbial mechanisms underlying the effects of straw addition on N 2 O emissions were investigated by 56-day incubation of soil from a long-term (27-year) no-tillage (NoTill) and conventional tillage (ConvTill) field experiment. The abundance of N functional genes (amoA , amoB , nirK , nirS and nosZ) in no-tillage and conventional tillage soils was analysed based on straw addition. The application of 15N-labelled straw allowed us to trace N 2 O sources. Conventional tillage with 15N-labelled straw (ConvTill+Straw) reduced N 2 O emissions derived from soil by 42 %, whereas no-tillage with 15N-labelled straw (NoTill+Straw) reduced N 2 O emissions by only 8 % compared with soil without straw addition. The N 2 O emissions derived from straw were higher under NoTill+Straw than under ConvTill+Straw, whereas they accounted for only ~4 % of the total N 2 O emissions under both conditions. The nirK and nirS gene abundances were higher than those in soil without straw addition. Compared to that under ConvTill, the nosZ gene abundance was higher and the N 2 O emissions were 40 % lower under ConvTill+Straw, indicating its strong capacity to reduce N 2 O to N 2. Pathway analysis showed that gene (amoA and nirK) abundance combined with soil properties (particulate organic matter nitrogen (POMN) and NO 3 −) were the main factors affecting N 2 O emissions, with increased POMN and nirK abundance driving increased N 2 O production under NoTill+Straw. However, gene (amoA , amoB , nirS and nosZ) abundances affected N 2 O emissions, with the nosZ gene being the main factor decreasing N 2 O under ConvTill+Straw. These findings revealed that straw return suppressed N 2 O emissions in conventional tillage soil, which may mitigate greenhouse gas emissions. [Display omitted] • N 2 O emissions were similar between no-tillage and conventional tillage soils. • Straw input decreased N 2 O emissions derived from soil under both tillage practices. • Straw input increased nirK and nirS gene abundances under both tillage practices. • No-tillage soil resulted in greater N 2 Oemissions derived from straw than conventional tillage soil. • Reduced N 2 O emissions under ConvTill+Straw was due to the increased nosZ gene abundance. [ABSTRACT FROM AUTHOR]