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Root mucilage (RM), a soil-born biohydrogel, affects the physical stability of the rhizosphere. One reason for this is attributed to the present polysaccharides which contribute to the formation of aggregates by acting as interparticulate glue. The aim of this study was to explore how physico-chemical properties of polymers of interparticulate gels influence this gluing and thus soil microstructural stability. We hypothesized that the microstructural stability of sand increases with the viscosity of the amended biohydrogel, which depends on the content of carbohydrate polymers and non-esterified uronic acids which themselves determine the amount of absorbed calcium. Therefore, natural RM of maize and wheat were compared with higher viscous chia seed mucilage (SM) as a widely used model for RM, and with industrial pectin rich in uronic acids partially methylated. Results show that additionally to Ca binding by uronic acids, binding by proteins is a further possible mechanism of Ca adsorption in RM. Upon Ca addition, the viscosity increased upon intermolecular associations (pectin) and decreased upon suppression of intermolecular charge–charge repulsion (chia SM, maize RM). Amount of high-molecular weight material in the amendment affected strongly soil microstructural stability. Results further suggest the creation of gel micro-zones upon Ca addition, which increase the viscosity of interparticulate gel and sand microstructural stability. Finally, the study outlines several physico-chemical mechanisms through which interactions between biotic (roots and seed) and abiotic components (mineral particles) influence soil structure, which control the water, air and nutrient flow through the rhizosphere and is, thus, an important soil quality parameter. [ABSTRACT FROM AUTHOR]

Mucilage produced at the root tips is a soil-born biohydrogel, whose framework is a three-dimensional polysaccharidic polymer network, which can contain over 90% water. The specific biohydrogel properties of mucilage, such as volumetric expansion and shrinkage, affect soil mechanical and hydraulic properties. Still, the physico-chemical mechanisms governing the interactions between mucilage and the porous soil system remain mostly unclear. To our best knowledge, no currently applied method allows the distinction between biohydrogel phases and pore water in the porous soil system. In this work, we used 1 H NMR relaxometry to analyze the presence and properties of biohydrogels in soil. Mucilage in soil leads to a hierarchical pore structure, consisting of the polymeric biohydrogel network surrounded by the surface of soil particles. Water molecules entrapped in mucilage-containing soils revealed an accelerated bulk relaxation and a higher surface relaxivity in comparison with soils not containing mucilage. In model soils, we quantified the gel effect, here defined as the influence of mucilage on proton relaxation. The difference between transversal and longitudinal relaxation rates was plotted as a function of the reciprocal diameter of the model soil particles for soils containing and not containing mucilage. The gel effect was thereby characterized by an accelerated bulk relaxation and an accelerated surface relaxation , traduced respectively by an increased y-intercept and an increased linear coefficient for mucilage-containing soil. [ABSTRACT FROM AUTHOR]