Reactive Oxygen Species Promote Nitrous Oxide (NO) Emissions from Soil/Sediment during the Anoxic-Oxic Transition.

Reactive oxygen species (ROS)-induced element/pollutant geochemical processes in fluctuating anoxic-oxic areas have received increasing attention in recent years. Nitrous oxide (NO) is a strong greenhouse gas; however, the relationship between ROS and NO emissions in these areas has not been established. This work revealed the essential role of ROS in promoting NO emissions in soil/sediment during the anoxic-oxic transition. ROS decreased the rate of nitrate reduction by 26-31% and increased NO emissions by 8.8-31.3% (at 48 h). ROS-induced NO emission was via inhibiting the step of NO reduction. During the anoxic-oxic transition, the contribution of ROS to inhibit the step of NO reduction was higher than 52.6%, demonstrating the important role of ROS. The downregulated relative transcription of the gene demonstrated inhibition at the gene level. Hydrogen peroxide was the dominant ROS species inhibiting NO reduction, while the role of hydroxyl radicals was negligible, suggesting a different behavior of NO emission with common pollutant conversion induced by ROS during the anoxic-oxic transition. This study demonstrated an overlooked factor in promoting NO emission in the soil/sediment and appealed to a re-examination of the mechanism of NO emissions in fluctuating anoxic-oxic areas.