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A Molecular Investigation of Soil Organic Carbon Composition across a Subalpine Catchment

1
Department of Chemistry; Stanford University, Stanford, CA 94305, USA
2
Department of Earth System Science, Stanford University, Stanford, CA 94305, USA
3
U.S. Geological Survey, Denver, CO 80215, USA
4
Department of Geological Sciences, Stanford University, Stanford, CA 94305, USA
5
Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA
6
Rocky Mountain Biological Laboratory, Crested Butte, CO 81224, USA
*
Author to whom correspondence should be addressed.
Soil Syst. 2018, 2(1), 6; https://doi.org/10.3390/soils2010006
Received: 1 December 2017 / Revised: 12 January 2018 / Accepted: 25 January 2018 / Published: 1 February 2018
(This article belongs to the Special Issue Soil Organic Matter Dynamics)
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Abstract

The dynamics of soil organic carbon (SOC) storage and turnover are a critical component of the global carbon cycle. Mechanistic models seeking to represent these complex dynamics require detailed SOC compositions, which are currently difficult to characterize quantitatively. Here, we address this challenge by using a novel approach that combines Fourier transform infrared spectroscopy (FT-IR) and bulk carbon X-ray absorption spectroscopy (XAS) to determine the abundance of SOC functional groups, using elemental analysis (EA) to constrain the total amount of SOC. We used this SOC functional group abundance (SOC-fga) method to compare variability in SOC compositions as a function of depth across a subalpine watershed (East River, Colorado, USA) and found a large degree of variability in SOC functional group abundances between sites at different elevations. Soils at a lower elevation are predominantly composed of polysaccharides, while soils at a higher elevation have more substantial portions of carbonyl, phenolic, or aromatic carbon. We discuss the potential drivers of differences in SOC composition between these sites, including vegetation inputs, internal processing and losses, and elevation-driven environmental factors. Although numerical models would facilitate the understanding and evaluation of the observed SOC distributions, quantitative and meaningful measurements of SOC molecular compositions are required to guide such models. Comparison among commonly used characterization techniques on shared reference materials is a critical next step for advancing our understanding of the complex processes controlling SOC compositions. View Full-Text
Keywords: soil organic carbon; FT-IR; XAS soil organic carbon; FT-IR; XAS
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

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Hsu, H.-T.; Lawrence, C.R.; Winnick, M.J.; Bargar, J.R.; Maher, K. A Molecular Investigation of Soil Organic Carbon Composition across a Subalpine Catchment. Soil Syst. 2018, 2, 6.

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