Nitrifiers Drive Different N2O Production Patterns in Tropical River Sediments

Area of Science:

• Environmental Science
• Biogeochemistry
• Climate Change Research

Background:

• Global riverine nitrous oxide (N₂O) emissions have quadrupled since the 20th century.
• N₂O emissions from tropical rivers remain poorly understood, despite their potential significance.

Purpose of the Study:

• To investigate N₂O flux, production rates, and mechanisms in China's tropical rivers.
• To identify key microbial pathways and environmental factors controlling N₂O production in these ecosystems.

Main Methods:

• In situ N₂O flux measurements using closed chambers.
• Potential N₂O production rates assessed with biological inhibitors and ¹⁵N-¹⁸O double tracer techniques.
• Microbial community analysis via metagenomic sequencing and reverse transcription qPCR.

Main Results:

• Hainan rivers exhibit high N₂O flux and production rates, indicating they are significant emission hotspots.
• Estuary samples showed significantly higher N₂O flux and production rates compared to nonestuary samples.
• Nitrifier denitrification (ND) was the dominant N₂O production pathway, particularly in estuaries, involving specific ammonia-oxidizing bacteria and comammox.

Conclusions:

• Tropical rivers, especially estuaries, are critical sources of N₂O emissions.
• Nitrifier denitrification is a key microbial process driving N₂O production in these systems.
• Management strategies focusing on ammonium fertilizer and estuary restoration are crucial for mitigating tropical river N₂O emissions and global climate change.