Mapping the soil microbiome functions shaping wetland methane emissions.

Area of Science:

• Soil microbial ecology
• Biogeochemistry
• Environmental microbiology

Background:

• Freshwater wetlands are significant global methane sources, yet the microbial communities and processes responsible for methane emissions remain poorly understood.
• Understanding these microbial dynamics is crucial for climate change mitigation strategies.

Purpose of the Study:

• To investigate the microbial membership and methane production in a highly prolific US wetland over five years.
• To provide a genome-resolved understanding of microbial biogeochemical functions in wetland soils.
• To identify factors influencing methane hotspots and microbial activity patterns.

Main Methods:

• Collected over 700 soil samples for metagenomic and metatranscriptomic analysis.
• Constructed a catalog of 2,502 metagenome-assembled genomes (MAGs) from diverse bacterial and archaeal phyla.
• Integrated genomic data with 133 soil metatranscriptomes and in situ methane measurements.
• Analyzed microbial community structure and gene expression across spatial (depth) and temporal gradients.

Main Results:

• Identified 2,502 MAGs, including novel lineages, revealing microbial diversity in wetland soils.
• Found that centimeter-scale depth differences were the primary drivers of microbial community structure and function, surpassing land cover and temporal effects.
• Observed stable, depth-stratified transcriptional profiles of methane-cycling microorganisms, even after flooding-induced redox shifts.
• Linked co-expression patterns and depth-resolved methane data to specific metabolisms and trophic structures predictive of methane hotspots.

Conclusions:

• Wetland methane cycling is governed by stable, depth-stratified microbial activity, challenging the assumption that hydrological manipulations alone can control methanogenesis.
• Spatially organized microbial networks, including methanogens, methanotrophs, fermenters, and iron reducers, are key drivers of methane cycling.
• Highlights the limitations of genome-only studies and emphasizes the need for in situ activity measurements for effective wetland management and climate modeling.