Unveiling mysteries of micro-porous structures in xylem vascular of plants: characterising nutrient transport using electro-hydrodynamics

Abstract We unveil the flow and ionic transport characteristics of xylem vessels to establish a correlation between in situ electrical energy generation and plant bioregulation. Scanning electron microscopy of the vascular bundles of Brassica juncea provides detailed features of lumen diameter and the porous pit structures of xylem walls. To investigate the nutrient transport and in situ electrical energy generation, we develop a two-dimensional modelling framework of the xylem vessel that is aligned with the experimental data. The solid wall model of the xylem vessel significantly underestimates axial flow resistance at higher inlet pressures, especially for smaller lumen diameters. Within the considered inlet pressure range, the under-prediction in axial flow resistance ranges from 3.14 % to 6.78 % and 0.37 % to 1.19 % for lumen sizes of 5 $\mu$ m and 15 $\mu$ m, respectively. Our analysis manifests that radial transport of ionic nutrients improves with increased porosity and permeability of the pitted porous wall. In the range of inlet pressure under consideration, it is shown that radial efficiency increases by 793.2 % to 471.9 % when the lumen diameter is reduced from 15 $\mu$ m to 5 $\mu$ m. The increased radial flow efficiency in narrower xylem vessels may support plant survivability under drought stress. Remarkably, we demonstrate that it is not the electrical potential alone, but the combined electrical and hydraulic power that influences plant growth. The amplified hydraulic and electrical power in plants with larger xylem vessels may promote growth attributed to more efficient ionic nutrient transport. We establish that the ratio of specific hydraulic conductivity to electrical conductivity acts as a potential indicator of plant health. This ratio increases with root-side inlet pressure; nevertheless, its dependence on lumen diameter is non-monotonic. The insights gained from the current work may advance the understanding of how in situ electrical stimulation regulates plant bioactivities.