Linking subsurface biogeochemical nitrogen cycling to surface fluxes over a range of soil moisture conditions

Soil biogeochemical processes produce greenhouse gases which can have significant environmental impacts when exchanged with the atmosphere. The magnitude of surface fluxes is driven by vertical concentration gradients, thus understanding drivers of below-ground N₂O production and consumption pathways is critical to atmospheric greenhouse gas mitigation strategies. We present subsurface gas composition and surface flux measurements in laboratory soil mesocosms to understand how depth-dependent soil processes impact surface fluxes over a range of soil moisture conditions. Diffusive gas probes are buried at three depths in three mesocosms of Northeastern agricultural soil and the columns are capped for surface flux measurements. We measure N₂O (¹⁴N¹⁵NO, ¹⁵N¹⁴NO, ¹⁴N¹⁴NO, N₂¹⁸O), NO, CO₂ (¹²CO₂, ¹³CO₂), and O₂ coupled with soil moisture and temperature measurements using a Tunable Infrared Laser Direct Absorption Spectrometer (TILDAS). Isotopically resolved maps of trace gases in response to ¹⁵N-labled N₂O dosing under a range of soil moisture conditions at various subsurface depths provides insight into the impact of soil moisture and oxygen content on subsurface transport, abiotic transformations and biological processes impacting surface fluxes.