Preprints
https://doi.org/10.5194/bg-2021-295
https://doi.org/10.5194/bg-2021-295

  09 Nov 2021

09 Nov 2021

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

Soil geochemistry as a driver of soil organic matter composition: insights from a soil chronosequence

Moritz Mainka1, Laura Summerauer2, Daniel Wasner2, Gina Garland2,3, Marco Griepentrog2, Asmeret Asefaw Berhe4, and Sebastian Doetterl2 Moritz Mainka et al.
  • 1Institute of Landscape and Plant Ecology, Universität Hohenheim, Stuttgart, 70599, Germany
  • 2Department of Environmental System Science, ETH Zürich, Zürich, 8092, Switzerland
  • 3Agroscope, Soil Quality and Use group, 8046 Zurich, Switzerland
  • 4Department of Earth Sciences, Life & Environmental Sciences, University of California, Merced, 95343, USA

Abstract. A central question in carbon research is how stabilization mechanisms in soil change over time with soil development and how this is reflected in qualitative changes of soil organic matter (SOM). To address this matter, we assessed the influence of soil geochemistry on bulk SOM composition along a soil chronosequence in California, USA spanning 3 million years. This was done by combining data on soil mineralogy and texture from previous studies with additional measurements on total carbon (C), stable isotope values (δ13C and δ15N), and spectral information derived from Diffuse Reflectance Infrared Fourier-Transform Spectroscopy (DRIFTS). To assess qualitative shifts in bulk SOM, we analysed the peak areas of simple plant-derived (S-POM), complex plant-derived (C-POM), and predominantly microbially derived OM (MOM) and their changes in abundance across soils varying several millennia to millions of years in weathering and soil development. We observed that SOM became increasingly stabilized and microbially-derived (lower C : N ratio, increasing δ13C and δ15N) as soil weathering progresses. Peak areas of S-POM (i.e. aliphatic root exudates) did not change over time, while peak areas of C-POM (lignin) and MOM (components of microbial cell walls (amides, quinones, and ketones)) increased over time and depth and were closely related to clay content and pedogenic iron oxides. Hence, our study suggests that with progressing soil development, SOM composition co-varies with changes in the mineral matrix. Our study indicates that a discrimination in favour of structurally more complex OM compounds (C-POM, MOM) gains importance as the mineral soil matrix becomes increasingly weathered.

Moritz Mainka et al.

Status: open (until 29 Dec 2021)

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Moritz Mainka et al.

Moritz Mainka et al.

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Short summary
The largest share of terrestrial carbon is stored in soils making them highly relevant in regard of Global Change. Yet, the mechanisms governing soil carbon stabilization are not well understood. The present study contributes to a better understanding of these processes. We show that qualitative changes of soil organic matter (SOM) co-vary with alterations of the soil matrix following soil weathering. Hence, the type of SOM that is stabilized in soils might change as soils develop.
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