Nitrate Availability Modulates the Temperature Sensitivity of N₂O and N₂ Production From Denitrification

Nitrous oxide (N₂O) can be both produced and reduced to dinitrogen (N₂) during microbial denitrification, with the balance between these steps controlling the net flux of this potent climate gas. Here, we first used a meta-analysis of published studies to predict how warming may regulate N₂O and N₂ production in soils and sediments. However, as most of these former studies used nitrate at far higher than ambient concentrations, the applicability of these predictions to ambient conditions may be limited. In addition, few studies separated denitrification from other microbial pathways contributing to N₂O and N₂ production. To address these limitations, we used ¹⁵N-isotope labelling experiments in freshwater sediments to test how temperature sensitivity varies with limited (10 μM) and replete (100 μM) nitrate. Temperature affected N₂O and N₂ production only when nitrate was replete, where N₂ production increased but net N₂O production declined with warming, leading to a lower N₂O:N₂ production ratio at higher temperatures. These results show that substrate availability can outweigh temperature in controlling the balance between N₂O and N₂ production, indicating that temperature-based predictions of N₂O emissions alone may overestimate the effects of climate warming.