Metaproteomics-informed stoichiometric modeling reveals the responses of wetland microbial communities to oxygen and sulfate exposure

Climate changes significantly impact greenhouse gas emissions from wetland soil. Specifically, wetland soil may be exposed to oxygen (O₂) during droughts, or to sulfate (SO₄^2-) as a result of sea level rise. How these stressors – separately and together – impact microbial food webs driving carbon cycling in the wetlands is still not understood. To investigate this, we integrated geochemical analysis, proteogenomics, and stoichiometric modeling to characterize the impact of elevated SO₄^2- and O₂ levels on microbial methane (CH₄) and carbon dioxide (CO₂) emissions. The results uncovered the adaptive responses of this community to changes in SO₄^2- and O₂ availability and identified altered microbial guilds and metabolic processes driving CH₄ and CO₂ emissions. Elevated SO₄^2- reduced CH₄ emissions, with hydrogenotrophic methanogenesis more suppressed than acetoclastic. Elevated O₂ shifted the greenhouse gas emissions from CH₄ to CO₂. The metabolic effects of combined SO₄^2- and O₂ exposures on CH₄ and CO₂ emissions were similar to those of O₂ exposure alone. The reduction in CH₄ emission by increased SO₄^2- and O₂ was much greater than the concomitant increase in CO₂ emission. Thus, greater SO₄^2- and O₂ exposure in wetlands is expected to reduce the aggregate warming effect of CH₄ and CO₂. Metaproteomics and stoichiometric modeling revealed a unique subnetwork involving carbon metabolism that converts lactate and SO₄^2- to produce acetate, H₂S, and CO₂ when SO₄^2- is elevated under oxic conditions. This study provides greater quantitative resolution of key metabolic processes necessary for the prediction of CH₄ and CO₂ emissions from wetlands under future climate scenarios.