N2O isotopic composition and soil microclimate for grassland monoliths subjected to an experimental drought

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.