Publication abstract: Nitrous oxide is a powerful greenhouse gas whose atmospheric growth rate has increased rapidly over the past decade. Causes of N2O emission dynamics from terrestrial ecosystems and their responses to climate change remain poorly understood. Based on high-resolution isotopic measurements we found that microbial functional gene abundances and soil moisture were the main drivers of variability in baseline emissions and pathways. After fertilization and, surprisingly, under drought, denitrification dominated grassland N2O production and dynamics, contributing 70% of emissions. Drought responses of N2O emissions were supported by a clear reversible enrichment in nitrogen-bearing organic matter compared to oxygen on the surface of soil microaggregates. We observed hysteresis for both total N2O flux and denitrification contribution during rewetting, which were higher than control and drought for the same soil moisture range. These results illustrate that the magnitude of feedbacks between climate change and N2O emission pathways is sufficient to account for increases in atmospheric growth rate in the past decade. We expect these effects will be amplified in the coming decades as climatic extremes are expected to increase in severity.

Supplement to: Harris, Eliza; Diaz-Pines, E; Stoll, E; Schloter, Michael; Schulz, Stefanie; Duffner, C; Li, K; Moore, K L; Ingrisch, Johannes; Reinthaler, D; Zechmeister-Boltenstern, S; Glatzel, Stephan; Brüggemann, Nicolas; Bahn, Michael (2021): Denitrifying pathways dominate nitrous oxide emissions from managed grassland during drought and rewetting. Science Advances, 7(6), eabb7118