Soil N intensity as a measure to estimate annual N2O and NO fluxes from natural and managed ecosystems

As natural and managed terrestrial ecosystems are major sources of the potent greenhouse gas nitrous oxide (N2O) and of the atmospheric pollutant nitric oxide (NO), predicting the source strengths of these ecosystems is central to understanding and sustainably managing the N-oxides fluxes. Here we reviewed 82 high temporal resolution datasets on N2O and 57 on NO fluxes collected from multi-site and multi-year field measurements, including grasslands, forests, and agricultural crops, to assess whether soil N intensity, that is, the time-weighted sum of soil NH4+ and/or NO3- concentrations, can be used to estimate annual N-oxides emissions. We show that soil N intensity alone can accurately predict annual N2O and NO emissions, and that the N2O emission strength is exponentially related to the soil inorganic N load. Thus, measuring soil inorganic N loads should improve current estimates of N-oxide emissions from global terrestrial ecosystems, and open possibilities for monitoring N2O mitigation efforts.