Elevated atmospheric CO2 increases N2O emissions when soil nitrate is high

Background/Question/Methods:

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). 

Results/Conclusions:

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.