Nitrous oxide sources, mechanisms and mitigation

Atmospheric nitrous oxide (N₂O) is a potent greenhouse gas and ozone-depleting substance. In this Review, we outline global N₂O sources, with a focus on hotspots and hot moments, and discuss strategies to mitigate N₂O emissions. N₂O can be released by natural sources such as bedrock weathering, but anthropogenic sources such as agriculture account for 40% of total emissions. Hotspots are localized regions of high emissions and include cropland soils (2.1 Tg N yr⁻¹), tropical forests (1.55 Tg N yr⁻¹), pasture soils with animal waste return (1.7 Tg N yr⁻¹), and streams and small lakes (0.4 Tg N yr⁻¹). Brief periods of intense emissions, known as hot moments, include post-deforestation, upland soils after fertilizer application, and desert and grasslands after precipitation. N₂O production from terrestrial and aquatic environments is mainly driven by two microbial processes: nitrification and denitrification. Bioaugmentation and biogeoengineering technologies hold potential for reducing N₂O emissions; for example, nature-based anammox hotspot geoengineering in Jiaxing, China, reduces N₂O emissions by 27.1%. However, the spatiotemporal heterogeneities and different production pathways of N₂O emissions are poorly represented in existing models, hindering the quantification and mitigation of emissions. A global N₂O database is needed to address this limitation. Additionally, artificial intelligence technology could enable real-time agricultural management to align nitrogen supply with crop demand.