Release Potential Of Nitrous Oxide From Soils And River Sediments In Beijing

Nitrous oxide（N₂O）is a powerful greenhouse gas with a great contribution to strengthening the global greenhouse effect.Soil is the main source of N₂O release,and N₂O released from farmland accounts for more than 60%of soil release.The research on N₂O production from farmland soil and agricultural river area has reference significance for exploring the generation mechanism of N₂O and controlling greenhouse gas emission.This study collected 20 vertical samples in summer and winter in Yanqing,Beijing,and24 samples of farmland soil along river banks,sediment and riparian soil in wet and dry seasons.The mechanism and influencing factors of N₂O production were studied by physical and chemical factor analysis,acetylene inhibition test,isotope tracer experiment by ¹⁵N and ¹8O and macro gene data analysis.The main conclusions are as follows:（1）Microbial processes are the main way of producing N₂O in soils and sediments.The nitrification process is the main process in the dry season of farmland and rivers,while the denitrification process is the main process in the wet season.The wet season is the main period for the production of N₂O in agricultural river area.The ammonia-driven process is the main process of N₂O generation in farmland soil,and the contribution rate varies from 85.30%to 87.98%,and the overall contribution rate is in the order of ND>NN>NCD>HD.（2）The N₂O production of farmland soil in non-river area has no significant correlation with physical and chemical factors.The production of N₂O in agricultural river area has a very significant negative correlation with water content and TOM,and a very significant positive correlation with p H and ammonium nitrogen.The water content was positively correlated with TOM and ammonium nitrogen,and the ammonium nitrogen in farmland was positively correlated with water content and TOM,but negatively correlated with river sediments and riparian soils.（3）The abundance of functional genes in the sediments and riparian soils of farmland soils and agricultural river areas is HD/NCD>ND>NN,but the abundance of functional genes of ammonia catalysis process that determine N₂O production is bigger than nitrate catalysis process,and abundance of functional genes of farmland soil in non-river areas is in the order of surface layer in summer>surface layer in winter>deep layer in summer>deep layer in winter.（4）Bacteria are the main microorganisms in soils and sediments.Alphaproteobacteria,Actinobacteria,Gammaproteobacteria and Betaproteobacteria are the dominant bacteria at class level in non-river area.Proteobacteria,Acidobacteria and Actinobacteria are the dominant bacteria at phylum level in the river area.The relative abundances of functional bacteria at genus level related to N₂O production are as follows:NN/AMO/ND-related bacteria>HD-related bacteria>ND-related bacteria>NCD-related bacteria>AMO-related bacteria.The river bacteria are dominated by nitrifying bacteria,but the abundance of denitrifying bacteria and aerobic denitrifying bacteria increased in the sediments.（5）The dominant bacteria at phylum level of farmland soil in non-river areas are not significantly correlated with environmental factors.Nitrate nitrogen and TOM are the two environmental factors that had the greatest impact on the structure of river microbial flora.Ammonium nitrogen and nitrate nitrogen are the main environmental factors affecting the microbial abundance related to N₂O production in non-river areas,and water content is the main environmental factor affecting the bacteria that produce N₂O in soil and sediments in the coastal zone.