Preprints
https://doi.org/10.5194/bg-2020-465
https://doi.org/10.5194/bg-2020-465

  17 Dec 2020

17 Dec 2020

Review status: this preprint is currently under review for the journal BG.

Reviews and syntheses: Heterotrophic fixation of inorganic carbon – significant but invisible flux in global carbon cycling

Alexander Braun1, Marina Spona-Friedl1, Maria Avramov1, Martin Elsner1,2, Federico Baltar3, Thomas Reinthaler3, Gerhard J. Herndl3,4, and Christian Griebler1,3 Alexander Braun et al.
  • 1Helmholtz Zentrum München, Institute of Groundwater Ecology, Ingolstaedter Landstrasse 1, D-85764 Neuherberg, Germany
  • 2Technical University of Munich, Department of Analytical Chemistry and Water Chemistry, Munich, Germany
  • 3University of Vienna, Department of Functional and Evolutionary Ecology, Althanstrasse 14, 1090 Vienna, Austria
  • 4Department of Marine Microbiology and Biogeochemistry, Royal Netherlands Institute for Sea Research, Utrecht University, PO Box 59, 1790 AB Den Burg, The Netherlands

Abstract. Heterotrophic CO2 fixation is a significant, yet underappreciated CO2 flux in the global carbon cycle. In contrast to photosynthesis and chemolithoautotrophy – the main recognized autotrophic CO2 fixation pathways – the importance of heterotrophic CO2 fixation remains enigmatic. All heterotrophs – from microorganisms to humans – take up CO2 and incorporate it into their biomass. Depending on the available growth substrates, heterotrophic CO2 fixation contributes at least 2–8 % and in the case of methanotrophs up to 50 % of the carbon building up their biomass. Assuming a standing stock of global heterotrophic biomass of 47–85 Pg C, we estimate that up to 7 Pg C have been derived from heterotrophic CO2 fixation and up to 20 Pg C yr−1 originating from heterotrophic CO2 fixation are funneled into the global annual heterotrophic production of 34–245 Pg C yr−1. These first estimates on the importance of heterotrophic fixation of inorganic carbon indicate that this carbon fixation pathway should be included in present and future global carbon budgets.

Alexander Braun et al.

 
Status: final response (author comments only)
Status: final response (author comments only)
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

Alexander Braun et al.

Alexander Braun et al.

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Short summary
It is known that of CO2 by photoautotrophic organisms is the major sink from the atmosphere. While microbiologist and physiologists are aware that CO2 fixation also occurs in heterotrophic organisms, this route of inorganic carbon, and its quantitative role is hardly recognized in biogeochemistry. We demonstrate that a huge amount of CO2 is fixed annually through anaplerotic reactions in heterotrophic organisms, and a significant quantity of inorganic carbon is temporally sequestered biomass.
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