Reactive Oxygen Species Promote Nitrous Oxide (N 2 O) 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 (N 2 O) is a strong greenhouse gas; however, the relationship between ROS and N 2 O emissions in these areas has not been established. This work revealed the essential role of ROS in promoting N 2 O emissions in soil/sediment during the anoxic-oxic transition. ROS decreased the rate of nitrate reduction by 26-31% and increased N 2 O emissions by 8.8-31.3% (at 48 h). ROS-induced N 2 O emission was via inhibiting the step of N 2 O reduction. During the anoxic-oxic transition, the contribution of ROS to inhibit the step of N 2 O reduction was higher than 52.6%, demonstrating the important role of ROS. The downregulated relative transcription of the NosZ gene demonstrated inhibition at the gene level. Hydrogen peroxide was the dominant ROS species inhibiting N 2 O reduction, while the role of hydroxyl radicals was negligible, suggesting a different behavior of N 2 O emission with common pollutant conversion induced by ROS during the anoxic-oxic transition. This study demonstrated an overlooked factor in promoting N 2 O emission in the soil/sediment and appealed to a re-examination of the mechanism of N 2 O emissions in fluctuating anoxic-oxic areas.