Wetlands encompass very diverse ecosystems, from ponds to peatlands, and are key ecosystems in the regulation of the carbon cycle on Earth. They store vast amounts of carbon, via organic matter burial, while being the largest non-anthropogenic source of methane emissions worldwide. However, we are currently unable to determine the future fate of carbon in these ecosystems because of our lack of understanding of the microbial metabolisms processing organic matter in the wetland (sub)soil. This talk will highlight recent results obtained from a continental wetland in France. It will, in particular, shed light on a novel archaeal phylum, Candidatus Bathyarchaeota, which was recently observed to predominate in wetland subsoils worldwide and whose carbon metabolisms are so far unknown.