Nitrous oxide sources, mechanisms and mitigation

Abstract

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. Nitrous oxide (N2O) emissions are continuously increasing owing to human activities. This Review discusses the temporal and spatial variability of N2O sources, N2O production pathways, and the potential of biogeoengineering strategies in agricultural soils and terrestrial water bodies to mitigate emissions.