Investigating the ecological controls on methane production in a riparian cottonwood forest and adjacent river

Abstract

This study explored how the chemical nature of organic matter may drive microbial communities and their metabolic processes of methane production in the Oldman River sediment and adjacent riparian cottonwood tree stems in southern Alberta. Carbon (C) and nitrogen (N) content in tree stems and river sediment environments were measured, while molecular genetic techniques and stable carbon isotope measurements were used to explore the microbial communities and methane production pathways. River sediment organic matter had lower C/N ratios than in tree stems, likely forming different substrates for microbial growth, resulting in contrasting microbial communities and greater microbial diversity observed in river sediments than in tree stems. The microbial communities differed in their metabolic pathways, with methane produced in tree stems occurring primarily through CO2 reduction, while river sediments produced more methane through acetate fermentation. This study highlights distinct microbial communities and metabolic pathways contributing to net ecosystem methane emission.