Formation of viscoelastic liquid bridges in the soil by drying of root mucilage

Plant roots secrete mucilage, a gel-forming polymer solution mainly composed of polysaccharides, which facilitates numerous physicochemical interactions between the plant and the soil. Soil granules near the root are tightly adhered to the root surface due to microscopic liquid bridges formed by the mucilage deposition. This zone of soil particles adhering to the root surface, called rhizosheath, has been actively studied so far. However, fundamental understanding of how the viscoelasticity of root mucilage generates different types of liquid bridges is still far from clear. Here we study the formation and instability of various types of viscoelastic liquid bridges formed by root mucilage. Unlike liquid bridges formed by Newtonian liquids, the viscoelastic liquid bridges stabilize the soil cohesion even when liquid volume fraction is severely low or the distance between soil particles is increased. Because of these characteristics, the contact between the root and the soil can be maintained in drying environment and subsequent root shrinkage. Our results can help one to understand the hydrodynamic role of root mucilage and to think about its potential usage for artificial systems mimicking rhizosheaths.