Kleinskalige und dynamische Analyse der mikrostrukturellen Rhizo- und Drillosphäreneigenschaften: Porosität und Physikochemie sowie deren Bedeutung für Wurzelwachstum, Nährstoffspeicherung und -lieferung
Zusammenfassung der Projektergebnisse
The research summarized in this final report concentrates on the physico-chemical parametrization of single biopores which had been classified into three different types: Colonized and/or created by a plant root (Cichorium intybus L., (R); by an earthworm (Lumbricus terrestris, (EW) or by a plant root followed by short-term colonisation of L. terrestris, (REW)). The experiments have been carried out in a new experimental approach (Central Pore Experiment, CePoX) hosted on CeFiT-B, at the research station Campus Klein-Altendorf, on a treatment with three years of chicory growth. Measurements were performed on undisturbed soil samples that were excavated from two depths in the Bt horizon of a Luvisol derived from loess in four pits, differing markedly in their general soil parameters. General soil parameters were determined for each pit and each depth, although based on strong statistical rules they cannot be defined as real replications and were therefore not helpful for the applied statistical models/analyses. Irrespective of this preface, the carried out statistical tests proofed that some of the investigated parameters differed significantly in dependency of the history of the biopore walls, and/or between the biopore walls and their surrounding matrices: The chemical composition in terms of hydrophobic (alkylic, C-H) and hydrophilic (carboxylic & carbonylic, C=O) functional groups (A/B-ratio), for example, depended on the distance from the biopore wall, the history of the biopore wall and on the investigated depth. Furthermore, we could link the A/B-ratio, of both biopore walls and soil matrices, to contact angles (CA) determined with the Sessile Drop method (SDM, additional work) and the Wilhelmy-plate method (WPM), while the linkage to CA derived from sorptivity tests failed. The latter one was caused by several methodological reasons, discussed more in detail in Haas et al. 2017 (we assume the dissolution of organic substances by ethanol). The statistical analysis showed the same influences for the soil relative diffusion coefficient (Ds/Do). In general, both parameters (A/B-ratio and Ds/Do) showed their largest values for the surface of the biopore wall, but whenever the biopore wall had been influenced by an earthworm or by a combined root and earthworm (EW and REW) lowest values for Ds/Do can be found at the surface of the biopore wall. Rheological measurements with biological model substances confirmed the alteration of biopore walls caused by biological processes. To obtain profound knowledge about the flow properties of the soil solution we cultivated the rhizobacterium Bacillus subtilis in aqueous solutions and determined their flow properties like surface tension and viscosity. A much more pronounced impact on the flow properties was observed than we had expected due to the alteration caused by inorganic ions (Holthusen et al., 2012c). The impact was most pronounced for the surface tension, since B. subtilis is known for its ability to produce surfactants. We highly recommend this kind of measurements with different types of soil microorganisms to link biological and physical processes. Overall, the results show clearly that soil properties of biopore walls differ from those of the bulk soil. Because of the importance as interface of the plant-soil-atmosphere continuum further research is needed to shed light on this highly altered and important soil volume, with a view to food security.
Projektbezogene Publikationen (Auswahl)
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Elastic and plastic soil deformation and its influence on emission of greenhouse gases. Journal of Institute of Agrophysics of Polish Academy of Sciences, Vol. 30. 2016, Issue 2, pp, 173–184.
Haas, C., D. Holthusen, A. Mordhorst, J. Lipiec, R. Horn.
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Controlled vertical stress in a modified amplitude sweep test (rheometry) for the determination of soil microstructure stability under transient stresses. Geoderma, Vol. 295. 2017, pp. 129-141.
Holthusen D., P. Pértile, J. Reichert, R. Horn
