Phytoscale Transport Physics: Insights into Xylem Flow Homeostasis and Drought Stress

TL;DR

This study combines experimental and computational methods to analyze how drought stress affects xylem vessel morphology and flow dynamics in Brassica juncea, revealing adaptations that enhance plant survival under water scarcity.

Contribution

It introduces a comprehensive framework integrating morphological measurements and numerical simulations to understand xylem flow adaptations during drought stress.

Findings

Drought reduces xylem diameter and pit size.

Drought decreases cellulose content, affecting elasticity and zeta potential.

Radial transport of nutrients increases under drought conditions.

Abstract

We investigate the flow dynamics of nutrient solution through the xylem vessels of Brassica juncea under drought stress. To this end, we perform experiments to obtain morphological traits of xylem vessels under drought-stressed conditions, and develop a mathematical framework to model the underlying flow through the xylem, considering several features relevant to the plant system. Performing experiments using state of the art instruments, we measure the morphology of xylem vessels, physicochemical and mechanical properties of xylem walls under drought stressed conditions. Our experimental results unveil that drought reduces both xylem diameter and pit aperture size, implicating hydraulic adaptations of plants to drought stress. We find that the reduced cellulose content in drought stressed xylem vessels lowers the zeta potential and decreases elasticity of the vascular region. Additionally, drought stress alters metabolite activity, increases reactive oxygen species, reduces chlorophyll content, and limits the uptake of essential metallic nutrients. Besides, we perform three-dimensional numerical simulations to evaluate local flow field, mechanical stress, hydraulic conductivity, and radial transport efficiency of xylem vessels under drought stressed conditions. Simulated results reveal that under drought conditions, resistance to axial flow through xylem vessels increases significantly, which in turn, promotes radial transport of nutrients, allowing plants to survive even in drought stress. We show that the radial flow efficiency of xylem vessels becomes notably higher under drought stress than in well-watered control plants. Overall, results of this endeavor provide new insights into how geometric adaptations of xylem vessels modify flow behavior under water deficient conditions, enhancing the plants ability to survive environmental stress.