Historical soil drainage mediates the response of soil greenhouse gas emissions to intense precipitation events

Precipitation events are increasing in intensity in the Midwestern US due to climate change. This is resulting in flooding of poorly-drained upland soils, which can feed back on climate change by altering greenhouse gas (GHG) emissions, including nitrous oxide (N ₂ O) and carbon dioxide (CO ₂ ). The objective of this study was to determine if soil drainage history affects the response of soil GHG emissions to rain events. To do this, we measured N ₂ O and CO ₂ fluxes from poorly-drained (PD) and well-drained (WD) soils in an agricultural field in Urbana, Illinois before and after large rain events. We also performed a lab experiment to separate effects of soil drainage history from contemporary effects of ponding. Finally, we utilized stable isotope techniques to measure gross N ₂ O dynamics and to determine the contributions of nitrifiers and denitrifiers to net N ₂ O fluxes. We found that ponding of WD soils led to pulses of net N ₂ O efflux caused by stimulation of gross N ₂ O production by denitrifiers. In contrast, PD soils had high net N ₂ O effluxes only between large rain events, and gross N ₂ O production was inhibited following ponding. Soil CO ₂ efflux was greater from PD soils under lab conditions, but autotrophic respiration obscured this trend in the field. Soil GHG emissions were a result of different contemporary ponding status as well as historical soil drainage, suggesting that historical soil redox regimes regulate soil GHG dynamics in response to precipitation. These soil drainage legacy effects are likely important in predicting soil GHG feedback effects on climate change.