The coupling interaction of NO with NH or NO as an important source of NO emission from agricultural soil in the North China Plain.

NO plays a crucial role in regulating NO formation from the soil, while how it affects the production of soil NO is still not well understood. In this study, NO and NO emissions from an agricultural field of the North China Plain (NCP) were comparatively investigated under five different fertilizer treatments (NH, NO, NO, NH + NO and NO + NO). Additionally, soil NH, NO and NO concentrations and the abundance of functional genes associated with nitrogen cycling were also analyzed in the incubation experiment. The results showed that the NO average fluxes from the complex treatments of NO + NO were 1.4-2.4 times the sum of those from the separate treatments of NO and NO whereas from the complex treatments of NO + NH were a factor of 1-1.4 larger than those from the separate treatments of NO and NH, indicating the coupling interaction of NO with NH or NO makes a remarkable contribution to NO emission from the soil. Significant reduction of the activity of NO reductase was found in the soil with the addition of NO, which favored the accumulation of NO formed through nitrification of NH and denitrification of NO, resulting in relatively high NO emissions from the complex treatments. As the intermediate product of nitrification and denitrification, NO produced is also expected to interact with NH or NO to promote NO emission from the soil, especially during fertilization events when NO is easily accumulated due to the acceleration of the nitrification and denitrification processes.