Elevated atmospheric CO2 increases N2O emissions when soil nitrate is high
Nitrous oxide (N2O) is a potent greenhouse gas with a global warming potential of 300 times higher than carbon dioxide (CO2). Elevated CO2 often increases soil N2O emissions. However, the primary controlling factors are unclear. We examined the impact of nitrogen status (nitrogen source and quantity) on N2O emissions under elevated atmospheric CO2 concentration. Three nitrogen sources [ammonium sulfate, ammonium sulfate and dicyandiamide (a nitrification inhibitor), potassium nitrate] were examined, using three model plant species (wheat, tall fescue and clover). Atmospheric CO2 concentrations were controlled using continuously stirred tank reactor (CSTR) chambers at the USDA-ARS Air-Quality (ambient at 400 µmol mol-1 versus elevated at 580µmol mol-1).
Our results showed that N2O emissions were significantly higher with nitrate than ammonium inputs. N2O emissions were significantly higher under elevated than ambient CO2 when high soil nitrate was available. N2O emissions were very low when ammonium nitrogen was applied, regardless of the CO2 concentration. Together, these results suggest that under elevated CO2, new N management regimes need to be developed to better synchronize N release with plant demands.