Anticipated increases in precipitation intensity due to climate change may affect hydrological controls on soil N2O fluxes, resulting in a feedback between climate change and soil greenhouse gas emissions. We evaluated soil hydrologic controls on N2O emissions during experimental water table fluctuations in large, intact soil columns amended with 100 kg ha-1 KNO3-N. Soil columns were collected from three landscape positions that vary in hydrological and biogeochemical properties (N = 12 columns). We flooded columns from bottom to surface to simulate water table fluctuations that are typical for this site, and expected to increase given future climate change scenarios. After the soil was saturated to the surface, we allowed the columns to drain freely while monitoring volumetric soil water content, matric potential and N2O emissions over 96 h. Across all landscape positions and replicate soil columns, there was a positive linear relationship between total soil N and the log of cumulative N2O emissions (r2 = 0.47; P = 0.013). Within individual soil columns, N2O flux was a Gaussian function of water-filled pore space (WFPS) during drainage (mean r2 = 0.90). However, instantaneous maximum N2O flux rates did not occur at a consistent WFPS, ranging from 63% to 98% WFPS across landscape positions and replicate soil columns. In contrast, instantaneous maximum N2O flux rates occurred within a narrow range (-1.88 to -4.48 kPa) of soil matric potential that approximated field capacity. The relatively consistent relationship between maximum N2O flux rates and matric potential indicates that water filled pore size is an important factor affecting soil N2O fluxes. These data demonstrate that matric potential is the strongest predictor of the timing of N2O fluxes across soils that differ in texture, structure and bulk density.
All Science Journal Classification (ASJC) codes
- Global and Planetary Change
- Environmental Chemistry
- Environmental Science(all)