N2O Is an Important Piece of the Puzzle, but Seeing the Whole Picture Strengthens Denitrification Research

• Published in: Journal of geophysical research. Biogeosciences 2021-10, Vol.126 (10), p.n/a
• Main Author: Emmett, B. D.
• Format: Article
• Language: English
• Subjects: Agricultural land; Air recirculation; Aquatic environment; Atmospheric models; Cores; Denitrification; Ecosystem models; Environment models; Estimates; Farm buildings; Farming systems; Fluxes; Greenhouse gases; Hot spots; Nitrogen; Nitrogen cycle; Nitrous oxide; Ozone; Ozone depletion; Sediments; Soil; Soils
• ISSN: 2169-8953; 2169-8961
• DOI: 10.1029/2021JG006576

For decades, denitrification research has been limited by the challenge of measuring fluxes of N2 against a background of high atmospheric concentrations. The methods developed to overcome this challenge all have strengths and weaknesses. Weitzman et al. (2021, https://doi.org/10.1029/2020JG006234) demonstrate the potential of one technique, the Nitrogen‐Free Air Recirculation Method, to measure denitrification end‐products in relatively undisturbed soil cores. This work reinforces the importance of N2 as the primary end‐product of denitrification, accounting for over 86% of measured fluxes in all cores sampled, and reveals unforeseen hotspots of denitrification at depth in soil. These findings are consistent with a similar effort to improve estimates of N2O: N2O + N2 yield at the field scale that predicts N2 fluxes two to three times higher than predicted using previous estimates. By providing a more complete picture of N2O and N2 production in terrestrial systems, these efforts can strengthen denitrification research and support essential refinement of ecosystem models. The identification of unforeseen denitrification hotspots highlights the continued surprises of soil nitrogen cycle and should inspire mechanistic research into the biophysical drivers and communities that mediate denitrification hotspots. Plain Language Summary Denitrification is the primary means of removing excess nitrogen from soil, sediments, and aquatic systems, however, it can also lead to the release of nitrous oxide, a powerful greenhouse gas and ozone depleting substance. Total denitrification is difficult to measure because of the high concentrations of its primary end‐product, N2, in the atmosphere and this has limited our understanding of the fate of nitrogen added to agricultural systems. Recent articles have demonstrated the promise of one methodology, a nitrogen‐free recirculating air system to measure both N2O and N2 production in samples of agricultural soils. These articles have demonstrated that rates of denitrification in agricultural soils are likely higher than previously estimated and identified unforeseen hotspots of denitrification in soils. These advances will support future research and demonstrate an approach to support full accounting of the fate of nitrogen applied to agricultural soils. Key Points N2 is the primary end‐product of denitrification and accurate assessment of N2 flux is critical to understanding ecosystem nitrogen balances Improved measurement