How life shapes the liquid phase in soils

Soils are characterized by frequent fluctuations in water content, which alter the physical environment and growth conditions for life. Plant roots and bacteria are capable of buffering these fluctuations by releasing a diverse, highly polymeric blend of substances (e.g. EPS and mucilage). Here we explain how their physical properties impact soil water dynamics. Water adsorption, high viscosity and low surface tension of EPS and mucilage prevent the break-up of the liquid phase and enable the formation of an interconnected matrix that spans throughout porous media. This matrix enhances water retention, maintains the connectivity of the liquid phase, decreases vapor diffusivity and local drying rates, creating a hydrological niche for plant roots and bacteria. We propose that the exudation of viscous polymeric substances is a universal strategy of plants and bacteria to delay desiccation, ensure flow of water and nutrients during drying, and provide time for adaptation to abiotic stress.