Nitrous Oxide Production Potential And Microbial Driving Mechanisms In Dryland Farmland Soil

As an important greenhouse gas and ozone depleting substance,nitrous oxide(N₂O)has attracted more and more attention in the research of global climate change and ecological environment change.Farmland soil is the main emission source of agricultural N₂O,accounting for 60%of the global anthropogenic N₂O emissions.Although microbial driven nitrification and denitrification processes are known to be the main source of N₂O,the key biological mechanism of N₂O production and its interaction with environmental variables are still difficult to predict.Based on this,this study selected the farmland vertical soil(0?200cm)in Beijing,Shandong,Henan,Hunan and Guangzhou as the research object.The N₂O production potential and production pathway were measured by acetylene inhibition method and¹⁵N-¹⁸O isotope tracer technology,and the abundance changes of functional genes in different N₂O production pathways were analyzed by macrogenome sequencing technology to analyze the microbial mechanism of N₂O production in farmland soil.The results are as follows:On the spatial scale,N₂O production shows strong spatio-temporal heterogeneity in the vertical depth of farmland soil.The surface of dryland farmland soil is a hot area for N₂O production.The surface soil contributes 80%of N₂O production in vertical depth.With the increase of soil depth,the contribution rate of nitrification process and denitrification process to N₂O production shows a downward trend,and at the depth of40cm,the soil hardly produces N₂O.On the time scale,N₂O production in farmland soil has obvious seasonality.When summer(24?)is the heat generated by N₂O,the overall performance is"high in summer and low in winter".The variation trend of N₂O production in vertical depth of samples in winter and summer is similar.The N₂O production potential of summer samples was significantly higher than that of winter samples.The relative abundance of functional genes(hao,AOB-nor B,HD+NCD-nor B)that directly produce N₂O in summer samples was significantly higher than that in winter samples.It is also found that ammonium salt driven nitrification process is the main contributor to N₂O production in Dryland farmland soil.In vertical depth,nitrification process contributes 84%of N₂O production,especially in topsoil,accounting for 96.5%.The contribution rate of nd to N₂O is the highest,and the contribution rate of nitrifier denitrification(ND)to N₂O on the surface of dryland farmland soil is up to 88%.Statistical analysis showed that N₂O production,nitrification and denitrification potential of farmland soil were correlated with physical and chemical properties(MC,p H,NH₄⁺-N)and functional gene abundance(hao,nor B,nir K).Proteobacteria?Terrabacteria group and Bacteria incertae sedis are the key bacteria that dominate the nitrification process of farmland soil surface.This study fills the lack of people's understanding of the source of N₂O in farmland vertical soil,and plays a supplementary role to the theoretical system of nitrogen cycle.At the same time,it is of positive significance to evaluate agricultural greenhouse gas emissions in China.