Abstract
The terrestrial subsurface contains nearly all of Earth’s freshwater reserves and harbours the majority of our planet’s total prokaryotic biomass. Although genetic surveys suggest these organisms rely on in situ carbon fixation, rather than the photosynthetically derived organic carbon transported from surface environments, direct measurements of carbon fixation in the subsurface are absent. Using an ultra-low level 14C-labelling technique, we estimate in situ carbon fixation rates in a carbonate aquifer. We find these rates are similar to those measured in oligotrophic marine surface waters and up to six-fold greater than those observed in the lower euphotic zone. Our empirical carbon fixation rates agree with nitrification rate data. Metagenomic analyses reveal abundant putative chemolithoautotrophic members of an uncharacterized order of Nitrospiria that may be behind the carbon fixation. On the basis of our determined carbon fixation rates, we conservatively extrapolate global primary production in carbonate groundwaters (10% of global reserves) to be 0.11 Pg carbon per year. These rates fall within the range found for oligotrophic marine surface waters, indicating a substantial contribution of in situ primary production to subsurface ecosystem processes. We further suggest that, just as phototrophs are for marine biogeochemical cycling, such subsurface carbon fixation is potentially foundational to subsurface trophic webs.
| Original language | English |
|---|---|
| Journal | Nature Geoscience |
| Volume | 15 |
| Issue number | 7 |
| Pages (from-to) | 561-567 |
| ISSN | 1752-0894 |
| DOIs | |
| Publication status | Published - Jul 2022 |
Bibliographical note
Funding Information:We thank F. Gutmann, H. Minkmar, P. A. Figueroa‐Gonzalez and R. Lehmann for their assistance with sample preparation, collection and filtration. We also thank M. Nowak and J. Southon for advice regarding C-bicarbonate supplementation and quantification of AMS results, respectively. In addition, we thank I. Görlich and M. Groth from the Core Facility DNA sequencing of the Leibniz Institute on Aging—Fritz Lipmann Institute in Jena for their help with Illumina sequencing. This study is part of the Collaborative Research Centre AquaDiva of the Friedrich Schiller University Jena, funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation)—SFB 1076—project number 218627073. S.T., X.X. and V.F.S. acknowledge additional support from the European Research Council (Horizon 2020 Research and Innovation Programme, grant agreement 695101). M.T. gratefully acknowledges funding from the DFG under Germany’s Excellence Strategy—EXC 2051—project ID 390713860. T.L.V.B. and A.J.P. were supported by the Ministerium für Kultur und Wissenschaft des Landes Nordrhein-Westfalen (‘Nachwuchsgruppe Dr. Alexander Probst’). Climate chambers to conduct experiments under controlled temperature conditions were financially supported by the Thüringer Ministerium für Wirtschaft, Wissenschaft und Digitale Gesellschaft (TMWWDG; project B 715-09075). The scientific results have in part been computed at the High-Performance Computing (HPC) Cluster EVE, a joint effort of both the Helmholtz Centre for Environmental Research—UFZ ( http://www.ufz.de/ ) and the German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig ( http://www.idiv-biodiversity.de/ ). 14