The impact of mucilage exudate on root water uptake – Numerical study

Abstract:

For many years, the rhizosphere, which is the zone of soil in the vicinity of the roots and which is influenced by the roots, is known as a unique soil environment with different physical, biological and chemical properties than those of the bulk soil. Indeed, in recent studies it has been shown that root exudates and especially mucilage alter the hydraulic properties of the soil, and that drying and wetting cycles of mucilage result in non-equilibrium water dynamics in the rhizosphere. While there are experimental evidences and simplified 1D model for those concepts, an integrated model that considers rhizosphere processes with a detailed model for water and roots flow is absent. Therefore, the objective of this work is to develop a 3D physical model of water flow in the soil-plant continuum that take in consideration root architecture and rhizosphere specific properties.

We simulate wetting and drying cycles and examine the impact of various rhizosphere processes on water content distribution and root water uptake (RWU). For wetting, the model predict that after infiltration the rate of change in the rhizosphere water content is lower than in the bulk soil (due to non-equilibrium), but over time water infiltrated into the rhizosphere and eventually the water content in the rhizosphere became higher than in the bulk soil. For drying, the high water holding capacity of the rhizosphere, and the non-equilibrium between water content and water potential delay the onset of stress. Furthermore, when continues drying-wetting setup is examined, rhizosphere properties results in a lower fluctuation of the water content around the root. Overall, the model presented here is the first attempt to include rhizosphere specific processes within a detailed soil-plant water flow model. The model provides a tool to examine the impact of different rhizosphere processes on water dynamics and RWU under different irrigation practices.