Physical protection of lignin by organic matter and clay minerals from chemical oxidation |
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| Institution: | 1. Future Industries Institute (FII), University of South Australia, Mawson Lakes, SA 5095, Australia;2. Department of Geological Sciences, Indiana University, Bloomington, IN 47405, USA;3. Global Centre for Environmental Remediation, University of Newcastle, Callaghan, NSW 2308, Australia;4. Cooperative Research Centre for Contamination Assessment and Remediation of the Environment, ACT Building, University of Newcastle, Callaghan, NSW 2308, Australia;5. School of Agriculture, Food and Wine, University of Adelaide, Urrbrae, SA 5064, Australia;1. College of Land and Environment, Shenyang Agricultural University, Shenyang 110866, China;2. Key Laboratory of Forest Ecology and Management, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110016, China;3. Department of Biosystems Engineering and Soil Science, University of Tennessee, Knoxville 37996, USA;4. Soil Science of Temperate Ecosystems, Büsgen-Institute, Georg August University of Göttingen, Büsgenweg 2, 37077 Göttingen, Germany;1. Natural Resources Canada, CanmetMINING, 555 Booth Street, Ottawa, Ontario, K1A 0G1, Canada;2. Department of Agronomy, Purdue University, 915 W State Street, West Lafeyette, IN, 47907, USA;1. Chair of Soil Science, Technical University of Munich, Emil-Ramann-Straße 2, 85354 Freising-Weihenstephan, Germany;2. Institute for Advanced Study, Technical University of Munich, Lichtenbergstraße 2a, 85748 Garching, Germany |
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| Abstract: | The role of organic matter (OM) concentration, structure and composition and how these relate to mineral protection is important for the understanding of long term soil OM dynamics. Various OM–clay complexes were constructed by sequential sorption of lignin and dodecanoic acid to montmorillonite. Humic acid–montmorillonite complexes were prepared at pH 4 and 7 to vary OM conformation prior to sorption. Results obtained with constructed OM–clay complexes were tested with isolated mineral fractions from two soils. Oxidation with an acidic NaClO2 solution was used to chemically oxidize lignin in the OM–clay complexes, sand-, silt- and clay-size soil fractions to test whether or not it can be protected from chemical attack. Gas chromatography–mass spectrometry was used to analyze lignin-derived phenols, cutin OH–acid (after CuO oxidation), fatty acid and n-alkanol concentrations and composition. We found that carbon content was not solely responsible for lignin stability against chemical oxidation. Lignin was protected from chemical oxidation through coating with dodecanoic acid and sorption of humic acid to clay minerals in a stretched conformation at pH 7. Therefore, interactions between OM constituents as well as OM conformation are important factors that protect lignin from chemical oxidation. Lignin-derived phenol dimers in the Grassland-Forest Transition soil fractions were protected from chemical oxidation to a greater extent compared to those in Grassland soil fractions. Therefore, although lignin was protected from degradation through mineral association, the extent of this protection was also related to OM content and the specific stability of lignin components. |
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