<p>Rhizosphere differs from bulk soil due to the presence of root mucilage, which affects physical, chemical, and microbial processes. It is well known that the rhizosphere responds slowly to water potential changes, which buffers changes in water content and helps keep the rhizosphere wetter than bulk soil during drying. Mucilage can affect solute transport and gas diffusion by affecting the distribution of liquid and gas phases. Despite increased recognition of the importance of mucilage, there still is a lack of models that describe the connectivity between different phases in the pore space of the rhizosphere during wetting and drying. The main challenge for model development is the complex concentration-dependent behaviour of mucilage. At low concentrations, mucilage is more like a liquid, whereas at higher concentrations, dry mucilage becomes a solid. In between, a viscoelastic state is observed where mucilage can be considered as a hydrogel.</p> <p>In previous work, we have developed a model based on a lattice spring method (LSM). This model was able to simulate the distribution of mucilage in the dry state at the pore scale. However, for wetter states, it is necessary to consider additional physical phenomena like surface tension, contact angle and viscoelasticity. In this study, we therefore aim to develop a Lattice-Boltzmann simulation framework to simulate two phase flow involving mucilage. To capture the interface between the two phases, a phase-field method will be used for interface tracking as this approach has gained considerable attention in recent years. The simulations will proceed as follows. We first assign the properties of a Newtonian fluid to the mixture of water and mucilage and calculate the equilibrium distribution of the liquid phase (mixture of water and mucilage) and gas in a simple pore geometry. Then, the water content will be gradually decreased, which will lead to an increase of mucilage concentration. This will in turn affect the viscosity, surface tension and contact angle, which will result in the emergence of the required viscoelastic behaviour of the mixture. For each of the water contents, the distribution of liquid (or hydrogel) and gas phases will be calculated.</p> <p>The newly developed model will provide us with new perspectives on hydrodynamic processes within the pore space of the rhizosphere. In addition, the model will help to better understand processes that strongly depend on hydraulic dynamics in the rhizosphere, such as solute transport, root penetration resistance, rhizosheath formation, and microbial activity.</p>
Compared with bulk soil, rhizosphere has different properties because of the existence of root mucilage, which affects physical, chemical, and microbial processes. The slow response of rhizosphere to changes in water potential buffers water content changes and leads the rhizosphere to be wetter than bulk soil during drying. By affecting connectivity of the liquid and gas phases, mucilage can also influence solute transport and gas diffusion. Overview of the literature and previous models shows the lack of a model that describes the connectivity between different phases in the rhizosphere pore space during wetting and drying processes. A major challenge is that mucilage shows a complex behavior, which at low concentrations is more like a liquid, whereas at higher concentration, dry mucilage becomes a solid. In between, a viscoelastic state is observed where mucilage can be considered as a hydrogel. In this study a three‐dimensional pore‐scale model based on the lattice spring method is introduced and used to simulate drying of mucilage between two soil particles. The model is capable of reproducing spider‐web‐like structures that are specific for mucilage. This three‐dimensional mucilage drying model is qualitatively validated via environmental scanning electron microscopy (ESEM) images of dry mucilage between glass beads. The proposed model may provide us with a new perspective on hydrodynamic processes within the pore space of the rhizosphere. In addition, the model may help to better understand further important processes that strongly depend on rhizosphere hydraulic dynamics, such as solute transport, connectivity of the liquid phase, root penetration resistance, rhizosheath formation, and microbial activity.
<p>Compared to bulk soil, rhizosphere has different properties because of the existence of root mucilage which affects the physical, chemical and also microbial processes. Hydraulic phenomena like limiting water flow at certain dry soil conditions, modulating extreme water contents by slow response to water potential changes; and also influencing solute transport and gas diffusion by varying the connectivity of liquid and gas phases are all classified under the set of the physical processes which are affected by mucilage in the rhizosphere.</p><p>Overview of the literature and previous models shows the lack of a three-dimensional pore-scale dynamic model for a better understanding of the connectivity between different phases during imbibition and drainage processes. A major challenge is that mucilage shows a complex behavior which at low concentrations is more like a liquid while at higher concentration when it is almost dry, it becomes a solid.</p><p>In particular, this study will use the Lattice Boltzmann method as a powerful tool for fluid dynamics study and the discrete element method for describing solids to present a pore-scale model for more accurate simulation and study of physical processes in the rhizosphere.</p>
Aims: Root exudates contain polymers that form crosslinks and can create a jelly-like substance named mucilage, which adheres to soil and thus promotes the formation of rhizosheath, i.e., of soil that remains attached to roots after gentle shaking. We hypothesized that rhizosheath formation shows an optimum at intermediate mucilage concentration and water content, but that its formation is limited at both high mucilage concentration and dryness as well as at low mucilage concentration and wetness. As parameters are difficult to control in real root-soil systems, we used an artificial root-soil-system where soil moisture and mucilage concentrations could be varied independently from one another in their effect on rhizosheath formation. Methods: Flax cords were disposed in sandy loam soil and in quartz sand, and in later study they were also amended to different moisture contents with five different concentrations of mucilage (from 0 to 0.2g dry mucilage g-1 water), isolated from chia and flaxseed mucilage after swelling of the respective seeds in distilled water for 15 min. Results: We found that in dry soil, rhizosheath formation peaked at intermediate mucilage concentration. This behavior was supported by our conceptual model of mucilage spreading and rhizosheath formation, which relies on a radial diffusion equation and assumes that at low mucilage concentration in the added water, molecule numbers are insufficient to support polymer-like networks that stick soil particles together. In a very concentrated gel, in turn, mucilage is too sticky to diffuse far into soil. Increasing soil moisture promotes rhizosheath formation both in low and high mucilage concentration range, though only to intermediate volumetric water contents of 0.15cm cm–3. Conclusions: We conclude that both water and mucilage concentration are important drivers in rhizosheath formation, but effects are not additive but can combine to an optimum range, with maximum rhizosheath here formed at 0.12 g mucilage g-1 rhizosphere water.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.