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

Abstract

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.