Changes in properties of soil-derived dissolved organic matter induced by biodegradation |
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Authors: | Karsten Kalbitz David Schwesig Juliane SchmerwitzKlaus Kaiser Ludwig HaumaierBruno Glaser Ruth EllerbrockPeter Leinweber |
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Affiliation: | a Department of Soil Ecology, Bayreuth Institute for Terrestrial Ecosystem Research (BITÖK), University of Bayreuth, Bayreuth D-95440, Germany b Soil Biology and Soil Ecology, Institute of Soil Science and Plant Nutrition, Martin-Luther-University Halle-Wittenberg, Weidenplan 14, D-06108 Halle (Saale), Germany c Institute of Soil Science and Soil Geography, University of Bayreuth, D-95440 Bayreuth, Germany d Institute of Soil Landscape Research, Centre for Agricultural Landscape and Land Use Research (ZALF), Eberswalder Straße 84, D-15374 Müncheberg, Germany e Institute of Soil Science and Plant Nutrition, University of Rostock, Justus-von-Liebig-Weg 6, D-18051 Rostock, Germany f IWW Rhenish-Westfalian Institute for Water Research, Moritzstr. 26, D-45476 Mülheim an der Ruhr, Germany |
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Abstract: | Properties of dissolved organic matter (DOM) determine its biodegradation. In turn, biodegradation changes the properties of the remaining DOM, which may be decisive for the formation of stable organic carbon in soil. To gain information on both mechanisms and controlling factors of DOM biodegradation and the properties of biodegraded DOM, we investigated changes in the composition of 13 different DOM samples extracted from maize straw, forest floors, peats, and agricultural soils during a 90-day incubation using UV absorbance, fluorescence emission spectroscopy, FTIR-spectroscopy, 1H-NMR spectroscopy, pyrolysis-field ionization mass spectroscopy (Py-FIMS), and 13C natural abundance before and after incubation. Changes in the DOM properties were related to the extent of biodegradation determined by the release of CO2. Increasing UV absorption and humification indices deduced from fluorescence emission spectra, and increasing portions of aromatic H indicated relative enrichment of aromatic compounds during biodegradation. This enrichment significantly correlated with the amount of DOC mineralized suggesting that aromatic compounds were relatively stable and slowly mineralized. 13C depletion during the incubation of highly degradable DOM solutions indicated an enrichment of lignin-derived aromatic compounds. Py-FI mass spectra indicated increasing contents of phenols and lignin monomers at the expense of lignin dimers and alkylaromatics during incubation. This partial degradation of higher-molecular, lignin-derived DOM compounds was accompanied by relative increases in the proportions of lower-molecular degradation products and microbial metabolites. Carbohydrates, especially when abundant at high initial contents, seem to be the preferred substrate for microorganisms. However, four independent methods suggested also some microbial production of carbohydrates and peptides during DOM degradation. After incubation, the composition of highly degradable DOM samples became similar to relatively stable DOM samples with respect to aromaticity, carbohydrate content, and thermal stability. We conclude that DOM biodegradation seems to result in organic matter properties being a precondition for the formation of stable carbon. These structural changes induced by DOM biodegradation should also result in stronger DOM sorption to the soil matrix additionally affecting DOM stabilization. |
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Keywords: | δ13C Degradation Dissolved organic matter Fluorescence spectroscopy 1H-NMR spectroscopy Pyrolysis-mass spectrometry Stabilization UV/VIS spectroscopy |
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