Nitrate availability modulates the temperature effect on N2O and N2 production from denitrification

Nitrous oxide (N2O) can be both produced and subsequently reduced to dinitrogen gas (N2) via canonical denitrification, making the balance between these steps a key control on the net flux of this potent climate gas. Through a meta-analysis, we showed that net N2O and N2 production from denitrification respond differently to temperature, exhibiting distinct temperature sensitivities. In addition, nitrate availability plays a critical role in regulating this balance, yet only few studies have examined the combined effects of temperature and nitrate availability in natural sediments. Using 15N-isotope labelling and anoxic sediment incubations, we found that temperature effects on N2O and N2 production from denitrification were evident only under high nitrate levels (100 {micro}M), while no significant temperature response occurred under low nitrate concentration (10 {micro}M). At high nitrate availability, N2 production increased at higher temperatures, whereas net N2O production declined, leading to a lower production ratio of N2O to N2 at warmer temperatures. These findings suggest that in nitrogen-limited ecosystems, substrate availability plays a stronger role than temperature in regulating denitrification. More broadly, they provide insights into how nutrient loading and climate warming interact to shape nitrogen cycling and greenhouse gas emissions in aquatic ecosystems.