Temperature differentially regulates estuarine microbial N₂O production along a salinity gradient

Area of Science:

• Environmental Science
• Microbiology
• Climate Science

Background:

• Nitrous oxide (N₂O) is a potent greenhouse gas affecting climate and ozone layers.
• Estuarine waters are significant sources of N₂O, influenced by ammonia oxidizers and denitrifiers.
• The specific role of temperature in regulating microbial N₂O production in these environments is not fully understood.

Purpose of the Study:

• To investigate the differential thermal responses of N₂O production in estuarine waters.
• To identify the microbial pathways and key genes involved in N₂O production and consumption under varying temperatures.
• To elucidate the combined effects of temperature and salinity on N₂O emissions.

Main Methods:

• Stable isotope labeling techniques (¹⁵N-labeled nitrite) were used to track N₂O production.
• Metatranscriptomic and metagenomic analyses were performed on enriched water samples.
• Measurements of optimal temperatures (T_opt) for N₂O production rates (N₂OR) were conducted in nearshore and offshore regions.

Main Results:

• N₂O production exhibited distinct thermal response patterns between nearshore and offshore estuarine sites.
• Optimal temperatures for N₂O production were higher in nearshore areas.
• Ammonia-oxidizing bacteria (AOB)-driven nitrifier denitrification was identified as the primary N₂O source, with its thermal tolerance increasing with salinity.
• Temperature influenced the expression of key genes (nirK, nosZ) involved in N₂O cycling, impacting overall emissions.

Conclusions:

• Temperature and salinity are critical regulators of N₂O production in estuarine systems, particularly concerning AOB activity.
• Understanding these microbial processes is crucial for predicting estuarine N₂O emissions under climate change scenarios.
• The study highlights the complex interplay of microbial communities and environmental factors in regulating greenhouse gas fluxes.