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Abstract:
There is only limited understanding of the impact of high p(CO2) on soil biomes. We have studied a floodplain wetland
where long-term emanations of temperate volcanic CO2 (mofettes) are associated with accumulation of carbon from the
Earth’s mantle. With an integrated approach using isotope geochemistry, soil activity measurements and multi-omics
analyses, we demonstrate that high (nearly pure) CO2 concentrations have strongly affected pathways of carbon
production and decomposition and therefore carbon turnover. In particular, a promotion of dark CO2 fixation significantly
increased the input of geogenic carbon in the mofette when compared to a reference wetland soil exposed to normal levels
of CO2. Radiocarbon analysis revealed that high quantities of mofette soil carbon originated from the assimilation of
geogenic CO2 (up to 67%) via plant primary production and subsurface CO2 fixation. However, the preservation and
accumulation of almost undegraded organic material appeared to be facilitated by the permanent exclusion of meso- to
macroscopic eukaryotes and associated physical and/or ecological traits rather than an impaired biochemical potential for
soil organic matter decomposition. Our study shows how CO2-induced changes in diversity and functions of the soil
community can foster an unusual biogeochemical profile.
