Soil N intensity as a measure to estimate annual N${}_2$O and NO fluxes from natural and managed ecosystems

As natural and managed terrestrial ecosystems are major sources of the potent greenhouse gas nitrous oxide (N${}_2$O) 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 N${}_2$O 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 NH${}_4$${}^{+}$ and/or NO${}_3$${}^{-}$ concentrations, can be used to estimate annual N-oxides emissions. We show that soil N intensity alone can accurately predict annual N${}_2$O and NO emissions, and that the N${}_2$O 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 N${}_2$O mitigation efforts.