O/N-alkyl and alkyl C are stabilised in fine particle size fractions of forest soils |
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Authors: | Email author" target="_blank">Ingo?Sch?ningEmail author Gerhard?Morgenroth Ingrid?K?gel-Knabner |
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Institution: | (1) Lehrstuhl für Bodenkunde, Department für Ökologie, Wissenschaftszentrum Weihenstephan für Ernährung, Landnutzung und Umwelt, D-85350 Freising-Weihenstephan, Germany;(2) Physikalisches Institut, Universität Erlangen-Nürnberg, D-91058 Erlangen, Germany |
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Abstract: | Carbon stocks and organic matter composition in bulk soils and particle size fractions of Ah horizons from Luvisols, Leptosols and Phaeozems under European beech (Fagus silvatica L.) forest were investigated by elemental analysis, solid state 13C nuclear magnetic resonance (13C CPMAS NMR) spectroscopy and lignin analysis (CuO-oxidation). Radiocarbon age was used as an indicator for C turnover. The SOM of bulk soils and particle size fractions is dominated by O/N-alkyl C and alkyl C. Compared to sand and silt fractions, clay fractions had lower C/N ratios and 14C abundances. Aryl C and more specifically phenolic components (O-aryl C) decreased from sand to clay fractions. The concomitant decrease of lignin, determined by CuO oxidation, suggests that a major proportion of O-aryl C can be attributed to lignin. Positive nonlinear relations between the O-aryl C and the C/N ratio reveal the trend of decreasing O-aryl C proportions with increasing decomposition. Although lignin is believed to be highly recalcitrant, only low amounts of lignin are found in the stable clay fractions. In contrast to O-aryl C, the O/N-alkyl C contribution decreased from sand to silt fractions, but increased again in the clay fractions, whereas alkyl C contents exhibited lowest values in the sand fractions. These results are indicative of stabilisation processes operating specifically on polysaccharides and alkyl C, but not on aryl C, through association with the clay fraction. |
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Keywords: | 13C CPMAS NMR Lignin Particle size fractionation Radiocarbon dating SOM Stabilisation |
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