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

## TL;DR

This study shows that nitrate levels strongly influence how warming affects the production of nitrous oxide and dinitrogen during denitrification in sediments.

## Contribution

The study demonstrates that nitrate availability can override temperature effects on N2O and N2 production ratios in denitrification.

## Key findings

- Under nitrate-replete conditions, warming increases N2 production while decreasing net N2O production.
- When nitrate is limited, temperature changes do not significantly affect N2O or N2 production.
- Nitrate availability can override temperature controls on the N2O:N2 production ratio.

## Abstract

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.

N2O is a potent greenhouse gas with denitrification in sediments and soils representing a major source, yet its response to warming under varying nitrate conditions remains poorly constrained. Combining meta‐analysis with isotope labelling experiments, we show that under nitrate‐replete conditions, warming increases production of climate‐benign N2 while decreasing net N2O production, lowering the N2O:N2 ratio. In contrast, when nitrate is limited, neither N2O nor N2 changes with warming. These findings show that nitrate availability can override temperature controls on N2O versus N2 partitioning, suggesting that ignoring nitrate availability may misrepresent future N2O emissions under global warming.