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The coupling interaction of NO2− with NH4+ or NO3− as an important source of N2O emission from agricultural soil in the North China Plain

Zhang, Yuanyuan, Guo, Guangxia, Wu, Hai, Mu, Yujing, Liu, Pengfei, Liu, Junfeng, Zhang, Chenglong
The Science of the total environment 2019 v.692 pp. 82-88
agricultural land, agricultural soils, ammonium, denitrification, fertilizer application, genes, greenhouse gas emissions, intermediate product, nitrates, nitric oxide, nitrification, nitrites, nitrogen cycle, nitrous oxide, nitrous oxide production, nitrous-oxide reductase, China
NO₂⁻ plays a crucial role in regulating N₂O formation from the soil, while how it affects the production of soil N₂O is still not well understood. In this study, N₂O and NO emissions from an agricultural field of the North China Plain (NCP) were comparatively investigated under five different fertilizer treatments (NH₄⁺, NO₃⁻, NO₂⁻, NH₄⁺ + NO₂⁻ and NO₃⁻ + NO₂⁻). Additionally, soil NH₄⁺, NO₂⁻ and NO₃⁻ concentrations and the abundance of functional genes associated with nitrogen cycling were also analyzed in the incubation experiment. The results showed that the N₂O average fluxes from the complex treatments of NO₂⁻ + NO₃⁻ were 1.4–2.4 times the sum of those from the separate treatments of NO₂⁻ and NO₃⁻ whereas from the complex treatments of NO₂⁻ + NH₄⁺ were a factor of 1-1.4 larger than those from the separate treatments of NO₂⁻ and NH₄⁺, indicating the coupling interaction of NO₂⁻ with NH₄⁺ or NO₃⁻ makes a remarkable contribution to N₂O emission from the soil. Significant reduction of the activity of N₂O reductase was found in the soil with the addition of NO₂⁻, which favored the accumulation of N₂O formed through nitrification of NH₄⁺ and denitrification of NO₂⁻, resulting in relatively high N₂O emissions from the complex treatments. As the intermediate product of nitrification and denitrification, NO₂⁻ produced is also expected to interact with NH₄⁺ or NO₃⁻ to promote N₂O emission from the soil, especially during fertilization events when NO₂⁻ is easily accumulated due to the acceleration of the nitrification and denitrification processes.