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 (O) during droughts, or to sulfate (SO) 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 SO and O levels on microbial methane (CH) and carbon dioxide (CO) emissions. The results uncovered the adaptive responses of this community to changes in SO and O availability and identified altered microbial guilds and metabolic processes driving CH and CO emissions. Elevated SO reduced CH emissions, with hydrogenotrophic methanogenesis more suppressed than acetoclastic. Elevated O shifted the greenhouse gas emissions from CH to CO. The metabolic effects of combined SO and O exposures on CH and CO emissions were similar to those of O exposure alone. The reduction in CH emission by increased SO and O was much greater than the concomitant increase in CO emission. Thus, greater SO and O exposure in wetlands is expected to reduce the aggregate warming effect of CH and CO. Metaproteomics and stoichiometric modeling revealed a unique subnetwork involving carbon metabolism that converts lactate and SO to produce acetate, HS, and CO when SO is elevated under oxic conditions. This study provides greater quantitative resolution of key metabolic processes necessary for the prediction of CH and CO emissions from wetlands under future climate scenarios.