Dynamic (redox) interfaces in soil - Carbon turnover in microbial biomass and flux into soil organic matter
Zusammenfassung der Projektergebnisse
The project investigated the fate and the role of microbial biomass residues, in particular bacterial cell envelope fragments, for the formation and properties of biogeochemical interfaces in soil. Our earlier finding that cell envelope residues are an important source for soil organic matter formation was supported by the slower mineralisation of cell envelope residues than of intact cells. The stability of cell envelope fragments was increased by co-precipitation with and thus encrustation in iron or aluminium oxyhydroxides. The encrusted cell envelope material was less accessible for degrading enzymes and its mineralisation was thus reduced. In the absence of oxygen, mineralisation of both intact cells and cell envelope fragments co-precipitated with iron oxyhydroxide increased, if the redox potential was sufficiently reduced by water logging plus addition of an easily available carbon source and nutrients. This resulted in reductive dissolution of iron oxyhydroxide and thus in a loss of the stabilising agent. In a chronosequence in the forefield of the Damma glacier, the number of potential cell envelope fragments increased during pedogenesis, based on scanning electron microscopy. This method, however, solely relies on fragment morphology and thus tends to overestimate their number. A combined analysis of morphology, attractive forces and thermal properties by atomic force microscopy-nanothermal analysis allowed identifying potential cell envelope fragments in soil samples more specifically. These analyses indicated that scanning electron microscopy in fact overestimated the number of cell envelope fragments in the samples, but confirmed the increase of cell envelope fragments during pedogenesis. Coverage of soil particles by cell envelope fragments can be assumed to change the surface properties of the particles (e.g. wettability) as these are determined by the material on the surface, e.g. organic coatings. The wettability of bacteria varies over a wide range, depending on the bacterial strain and the environmental conditions. For example. bacteria adapt to salt and water stress by increasing the hydrophobicity of their cell surface. Bacteria, in particular salt-stressed ones, attached to hydrophilic minerals decreased the wettability of the minerals depending on the cell number and on the wettability of the bacterial cells. Attachment of bacteria to soil particles may therefore play an important role in development of water repellency in soils. In summary, the project revealed some of the mechanisms involved in the stabilisation of bacterial cell envelope fragments in soil, and demonstrated that these fragments can have substantial influence on soil properties.
Projektbezogene Publikationen (Auswahl)
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(2012): SOM genesis: Microbial biomass as a significant source. Biogeochemistry 111: 41-55
Miltner A, Bombach P, Schmidt-Brücken B, Kästner M
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(2013): Live and death of streptomyces in soil – what happens to the biomass? Journal of Plant Nutrition and Soil Science 176: 665-673
Schütze, E, Miltner A, Nietzsche S, Achtenhagen J, Klose M, Merten D, Greyer M, Roth M, Kästner M, Kothe E
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(2013): Microbial cell-envelope fragments and the formation of soil organic matter - a case study from a glacier forefield. Biogeochemistry 113: 595-612
Schurig C, Smittenberg RH, Berger J, Kraft F, Woche SK, Göbel M-O, Heipieper HJ, Miltner A, Kästner M
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(2014): Bacterial impact on the wetting properties of soil minerals. Biogeochemistry 122: 269-280
Achtenhagen J, Goebel, MO, Miltner A, Woche SK, Kaestner M
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(2015): Methods for visualising active microbial benzene degraders in in situ microcosms. Applied Microbiology and Biotechnology 99: 957-968
Schurig C, Müller CW, Höschen C, Prager A, Kothe E, Beck H, Miltner A, Kästner M
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(2015): Microbial contribution to SOM quantity and quality in density fractions of temperate arable soils. Soil Biology and Biochemistry 81: 311-322
Ludwig M, Achtenhagen J, Miltner A, Eckhardt K-U, Leinweber P, Emmerling C, Thiele- Bruhn S
