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

Nitrous oxide (N2O) 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 N2O 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 N2O sources. Conventional tillage with 15N-labelled straw (ConvTill+Straw) reduced N2O emissions derived from soil by 42 %, whereas no-tillage with 15N-labelled straw (NoTill+Straw) reduced N2O emissions by only 8 % compared with soil without straw addition. The N2O emissions derived from straw were higher under NoTill+Straw than under ConvTill+Straw, whereas they accounted for only ~4 % of the total N2O 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 N2O emissions were 40 % lower under ConvTill+Straw, indicating its strong capacity to reduce N2O to N2. Pathway analysis showed that gene (amoA and nirK) abundance combined with soil properties (particulate organic matter nitrogen (POMN) and NO