pH selects for distinct N₂O-reducing microbiomes in tropical soil microcosms

Area of Science:

• Environmental Microbiology
• Biogeochemistry
• Genomics

Background:

• Nitrous oxide (N₂O) is a potent greenhouse gas and ozone-depleting substance.
• Microbial N₂O reduction to dinitrogen (N₂) by N₂O reductase (NosZ) is a key mitigation pathway.
• N₂O reduction at acidic pH remains poorly understood, particularly in tropical soils.

Purpose of the Study:

• To investigate the microbiology of N₂O reduction in acidic tropical soils.
• To identify microbial communities and genes involved in low pH N₂O mitigation.
• To explore the diversity of N₂O-reducing bacteria in acidic environments.

Main Methods:

• Incubation of acidic tropical soils (pH < 5) in microcosms with varying N₂O concentrations.
• Monitoring of N₂O consumption rates.
• Comparative metagenome analysis to identify dominant microbial taxa and functional genes (e.g., nosZ).

Main Results:

• N₂O was consumed in all microcosms, with longer lag times at higher N₂O concentrations.
• Distinct microbial communities (e.g., Peptococcaceae, Hyphomicrobiaceae) dominated acidic microcosms compared to circumneutral ones (Rhodocyclaceae).
• Metagenome-assembled genomes from acidic soils revealed novel Clade II nosZ-harboring bacteria, lacking nitrite reductase genes, indicating specialized N₂O reduction pathways.

Conclusions:

• Acidic tropical soils harbor diverse N₂O-reducing microbial communities, including novel taxa.
• The Clade II nosZ type is prevalent in acidic environments, suggesting adaptation to low pH N₂O reduction.
• These findings highlight the significant, yet underappreciated, role of acidic soils in global N₂O mitigation.