17 Dec 2020
17 Dec 2020
Reviews and syntheses: Heterotrophic fixation of inorganic carbon – significant but invisible flux in global carbon cycling
- 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
- 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.


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RC1: 'Review of Heterotrophic fixation of inorganic carbon', Anonymous Referee #1, 03 Jan 2021
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RC2: 'Review of Heterotrophic fixation of inorganic carbon', Anonymous Referee #2, 12 Feb 2021
Alexander Braun et al.
Alexander Braun et al.
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