Nitrous oxide is a powerful greenhouse gas whose atmospheric growth rate has accelerated over the past decade. Most anthropogenic N2O emissions result from nitrogen addition to soils through fertilization, which is converted to N2O via oxic nitrification and anoxic denitrification pathways. In situ, online isotopic measurements using spectroscopy can be used to understand soil N2O emission pathways and thus develop efficient, targeted mitigation strategies.

Isotopic measurements were used to understand N2O emission pathways under the influence of drought, which is expected to increase in frequency in many regions due to climate change. Drought-affected soils are expected to be well oxygenated; however, isotopic measurements showed that denitrifying pathways dominated N2O emissions during a severe drought applied to managed grassland. This was due to a reversible, drought-induced enrichment in nitrogen-bearing organic matter on soil microaggregates and suggested a strong role for chemo- or codenitrification. Throughout the post-drought rewetting period, denitrification dominated emissions, despite high variability in fluxes. Total N2O flux and denitrification contribution were significantly higher during rewetting than for control plots at the same soil moisture range. The observed feedbacks between precipitation changes induced by climate change and N2O emission pathways could account for some portion of the accelerating N2O growth rate observed over the past decade.