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Biogeosciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/bg-2020-308
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2020-308
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  26 Aug 2020

26 Aug 2020

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A revised version of this preprint was accepted for the journal BG.

Millennial-age GDGTs in forested mineral soils: 14C-based evidence for stabilization of microbial necromass

Hannah Gies1, Frank Hagedorn2, Maarten Lupker1, Daniel Montluçon1, Negar Haghipour1,3, Tessa Sophia van der Voort4, and Timothy Ian Eglinton1 Hannah Gies et al.
  • 1Department of Earth Sciences, ETH Zürich, Sonneggstrasse 5, 8092 Zürich, Switzerland
  • 2Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Zürcherstrasse 111, 8903 Birmensdorf, Switzerland
  • 3Laboratory of Ion Beam Physics, ETH Zürich, Otto-Stern-Weg 5, 8093 Zürich, Switzerland
  • 4Campus Fryslan, Rijksuniversiteit Groningen, Wirdumerdijk 34, 8911 CE Leeuwarden, the Netherlands

Abstract. Understanding controls on the persistence of soil organic matter (SOM) is essential to constrain its role in the carbon cycle and inform climate-carbon cycle model predictions. Emerging concepts regarding formation and turnover of SOM imply that it is mainly comprised of mineral-stabilized microbial products and residues, however, direct evidence in support of this concept remains limited. Here, we introduce and test a method for isolation of isoprenoid and branched glycerol dialkyl glycerol tetraethers (GDGTs) – diagnostic membrane lipids of archaea and bacteria, respectively – for subsequent natural abundance radiocarbon analysis. The method is applied to depth profiles from two Swiss pre-alpine forested soils. We find that the ∆14C values of these microbial markers markedly decrease with increasing soil depth, indicating turnover times of millennia in mineral subsoils. The contrasting metabolisms of the GDGT-producing microorganisms indicates it is unlikely that the low ∆14C values of these membrane lipids reflect heterotrophic acquisition of 14C-depleted carbon. We therefore attribute the 14C-depleted signatures of GDGTs to their physical protection through association with mineral surfaces. These findings thus provide strong evidence for the presence of stabilized microbial necromass in forested mineral soils.

Hannah Gies et al.

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Data Set – Millennial-age GDGTs in forested mineral soils Hannah Gies, Frank Hagedorn, Maarten Lupker, Daniel Montlucon, Negar Haghipour, Tessa Sophia van der Voort, Timothy Ian Eglinton https://doi.org/10.3929/ethz-b-000430425

Hannah Gies et al.

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Short summary
Understanding controls on the persistence of organic matter in soils is essential to constrain its role in the carbon cycle. Emerging concepts suggest that the soil carbon pool is predominantly comprised of stabilized microbial residues. To test this hypothesis we isolated microbial membrane lipids from two Swiss soil profiles and measured their radiocarbon age. We find that the ages of these compounds are in the range of millenia and thus provide evidence for stabilized microbial mass in soils.
Understanding controls on the persistence of organic matter in soils is essential to constrain...
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