Journal
GEODERMA
Volume 223, Issue -, Pages 54-61Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.geoderma.2014.01.028
Keywords
Soil organic matter; Chemical composition; Paleosol; Clay fraction; NMR
Categories
Funding
- National Science Foundation under Iowa State University [EAR 1226949]
- National Science Foundation under University of Iowa [EAR-1226412]
- National Science Foundation under University of Kansas [EAR-1226757]
- National Science Foundation under Old Dominion University [EAR1226323]
- Department of Agronomy, Iowa State University
- Department of Earth and Environmental Sciences
- Kansas Geological Survey,
- Old Dominion University Research Foundation
- Directorate For Geosciences
- Division Of Earth Sciences [1226757, 1226323] Funding Source: National Science Foundation
- Directorate For Geosciences
- Division Of Earth Sciences [1226412, 1226949] Funding Source: National Science Foundation
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Identifying which components of organic matter are preserved over millennia in paleosols is important for understanding the stabilization mechanisms of soil organic matter (SUM) and in evaluating the portion of the terrestrial carbon stock that might be attributed to paleosols. Using advanced solid-state nuclear magnetic resonance (NMR) techniques, we examined the chemical composition of clay-associated SUM in a chronosequence of four paleosols and one modern soil collected from a site in the eastern Great Plains in Kansas, USA. The NMR spectra of clay SUM of the paleosols indicated the presence of OCH and CH2 moieties, which represent polysaccharides and lipids, respectively. The paleosol SUM also showed an appreciable peptide component, as indicated by signals of NCH and N-C=0. As in the modem soil, lignin residues in the paleosols contributed little to the SUM, and condensed aromatics contributed modestly to the clay SOM. The Roberts Creek paleosol samples were exceptions. Their NMR spectra included a considerable nonprotonated aromatic carbon component, reflecting fused aromatic rings and suggesting the presence of clay-fraction charcoal residues, probably originating from paleofires. In the clay SUM of both the paleosols and the modern soil, the polysaccharides and peptides indicated by the NMR spectra are consistent with the presence of microbially derived peptidoglycan and perhaps chitin residues. We conclude that lipids, charcoal, and polysaccharides, probably in the form of microbial residues, are likely to be the dominant SOM components in the paleosol clay fractions. (C) 2014 Elsevier B.V. All rights reserved.
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