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

Area of Science:

• Environmental Science
• Microbiology
• Climate Science

Background:

• Nitrous oxide (N₂O) is a potent greenhouse gas, and its production and reduction to dinitrogen (N₂) during denitrification are key processes in the nitrogen cycle.
• Previous studies on warming effects on N₂O and N₂ production often used high nitrate concentrations, limiting applicability to ambient conditions.
• Distinguishing denitrification from other microbial pathways affecting N₂O and N₂ fluxes remains a challenge.

Purpose of the Study:

• To investigate the influence of temperature on nitrous oxide (N₂O) and dinitrogen (N₂) production under varying nitrate conditions.
• To assess the role of substrate availability in modulating temperature sensitivity of denitrification.
• To refine predictions of climate warming impacts on greenhouse gas emissions from soils and sediments.

Main Methods:

• Meta-analysis of existing literature on warming effects on N₂O and N₂ production.
• 15N-isotope labeling experiments in freshwater sediments to quantify N₂O and N₂ production.
• Controlled experiments varying nitrate concentrations (10 μM and 100 μM) and temperature.

Main Results:

• Temperature influenced N₂O and N₂ production significantly only under replete nitrate conditions (100 μM).
• With warming, N₂ production increased, while net N₂O production decreased under replete nitrate.
• The ratio of N₂O to N₂ production decreased at higher temperatures when nitrate was replete.

Conclusions:

• Nitrate availability can be a more critical factor than temperature in controlling the balance of N₂O and N₂ production.
• Temperature-driven predictions of N₂O emissions may overestimate the impact of climate warming, especially under low nitrate conditions.
• Understanding substrate-dependent microbial processes is crucial for accurate climate change impact assessments.