Journal cover Journal topic
Biogeosciences An interactive open-access journal of the European Geosciences Union
Journal topic
Volume 13, issue 22
Biogeosciences, 13, 6353–6362, 2016
https://doi.org/10.5194/bg-13-6353-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Biogeosciences, 13, 6353–6362, 2016
https://doi.org/10.5194/bg-13-6353-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 28 Nov 2016

Research article | 28 Nov 2016

Soil carbon dioxide emissions controlled by an extracellular oxidative metabolism identifiable by its isotope signature

Benoit Kéraval1,2,3, Anne Catherine Lehours1,2, Jonathan Colombet1,2, Christian Amblard1,2, Gaël Alvarez3,4, and Sébastien Fontaine3 Benoit Kéraval et al.
  • 1Clermont Université, Université Blaise Pascal, Laboratoire Microorganismes : Génome et Environnement, BP 10448, 63000 Clermont-Ferrand, France
  • 2CNRS, UMR 6023, Laboratoire Microorganismes : Génome et Environnement, 63178 Aubière, France
  • 3INRA, UR874 (Unité de Recherche sur l'Ecosystème Prairial), 5 Chemin de Beaulieu, 63039 Clermont-Ferrand, France
  • 4Clermont Université, VetAgro Sup, BP 10448, 6300 Clermont-Ferrand, France

Abstract. Soil heterotrophic respiration is a major determinant of the carbon (C) cycle and its interactions with climate. Given the complexity of the respiratory machinery, it is traditionally considered that oxidation of organic C into carbon dioxide (CO2) strictly results from intracellular metabolic processes. Here we show that C mineralization can operate in soils deprived of all observable cellular forms. Moreover, the process responsible for CO2 emissions in sterilized soils induced a strong C isotope fractionation (up to 50 ‰) incompatible with respiration of cellular origin. The supply of 13C glucose in sterilized soil led to the release of 13CO2 suggesting the presence of respiratory-like metabolism (glycolysis, decarboxylation reaction, chain of electron transfer) carried out by soil-stabilized enzymes, and by soil mineral and metal catalysts. These findings indicate that CO2 emissions from soils can have two origins: (1) from the well-known respiration of soil heterotrophic microorganisms and (2) from an extracellular oxidative metabolism (EXOMET) or, at least, catabolism. These two metabolisms should be considered separately when studying effects of environmental factors on the C cycle because the likelihood is that they do not obey the same laws and they respond differently to abiotic factors.

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Soil CO2 emissions are a major determinant of the carbon (C) cycle and its interactions with climate. Here, we show that soil CO2 emissions have two origins: (1) the well-known microbial cell respiration and (2) an extracellular oxidative metabolism (EXOMET) carried out by soil-stabilized enzymes and mineral catalysts. These two metabolisms have distinct C isotope signatures, allowing their detection in soil CO2 emissions.
Soil CO2 emissions are a major determinant of the carbon (C) cycle and its interactions with...
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