Investigating the Role of Bacillus Subtilis, a Plant Growth-Promoting Rhizobacteria, in Improving Soil Hydro-Physical Properties

摘要

Bacillus subtilis is a well-known plant growth promoting rhizobacteria. But research on its role in influencing hydro-physical properties of soil is still scarce. I conducted evaporation, percolation and pellicle experiments to better understand the underlying mechanisms through which the bacteria affected these processes. My research results showed reduced evaporation loss and increased water retention in the bacteria-treated sands. The percolation, evaporation, and drying front patterns confirmed the occurrence of steady diffusion-based upward and downward water flow mechanisms. The interplay of adsorption, viscosity, and surface tension of the bacterial EPS are likely the cause for the observations. In addition, SEM imaging and water repellency data suggested the occurrence of hydraulic stability rather than the mechanical stability in imparting such a result. Conversely, related research on EPS-mediated soil hydro-physical changes pivots around its hygroscopic nature and microstructure development to hold more water and reduce its loss. Our findings have broadened to the characterization of some important physical parameters i.e., surface tension, water repellency, and contact angle of the EPS that have a great implication in shaping the flow behavior of soil water. As a stress-tolerant bacterium, Bacillus subtilis adopts a cooperative locomotion and survival strategy by inter-changing surface tension and viscosity to cope with the fluctuating water conditions of the soil, which in-turn affects the hydraulic phenomenon of soil. Understand the ecological significance of such a strategy of Bacillus subtilis and identifying some key missing links of the important physiochemical properties of EPS to soil physics and hydraulics were the motivation of the current work. The research outcomes would contribute to the fundamental understanding of the effects of bacterial EPS on the hydro-physical properties of soil and thereby provide insights to effectively manage the green water in soil to achieve sustainability in agriculture.