Temperature differently affected methanogenic pathways and microbial communities in sub-Antarctic freshwater...

Area of Science:

• Environmental Science
• Microbiology
• Geochemistry

Background:

• Freshwater ecosystems contribute significantly to global methane (CH4) emissions.
• Global warming is expected to alter these emissions, impacting climate regulation.
• Sub-Antarctic lake sediments are understudied yet crucial in the methane cycle.

Purpose of the Study:

• To investigate temperature-induced changes in microbial community structure and methanogenic pathways in sub-Antarctic lake sediments.
• To quantify methane production rates (MPRs) under varying temperatures and precursor conditions.
• To assess the relative importance of different methanogenesis pathways (acetoclastic vs. hydrogenotrophic) with warming.

Main Methods:

• In situ CH4 flux measurements and laboratory incubations across a temperature gradient (5–20°C).
• Quantification of methanogenic gene abundance (mcrA) and methane production rates (MPRs).
• Microbial community structure analysis using 16S rRNA gene metagencing and precursor amendments (acetate, H2/CO2).

Main Results:

• A 5°C temperature increase doubled MPRs under unamended conditions, without altering overall microbial community structure.
• Acetate and H2/CO2 amendments significantly stimulated MPRs (up to 127-fold and 19-fold, respectively), with stronger enrichment of mcrA-carriers under acetate.
• Hydrogenotrophic methanogenesis contribution increased with temperature, and its temperature dependence was higher (1.92 eV) than acetoclastic (0.81 eV).
• Methanogenic archaeal community structure was driven by precursors, favoring Methanobacterium (H2/CO2) and Methanosarcina (acetate).
• Acetogenic H2 production outcompeted hydrogenotrophic methanogenesis at low temperatures.

Conclusions:

• Temperature alone does not shape total microbial community structure, which is site-specific.
• Increasing temperatures favor hydrogenotrophic methanogenesis over acetoclastic pathways in these sediments.
• Understanding these shifts is critical for predicting future methane emissions in a warming climate.