Preferential Root Tropisms in 2D Wet Granular Media with Structural Inhomogeneities

Cesare M Cejas,Raphaël Beaufret,Jean-Christophe Castaing,Christian Frétigny,Lawrence A Hough,Rémi Dreyfus

doi:10.1038/s41598-019-50653-8

Abstract

We investigate certain aspects of the physical mechanisms of root growth in a granular medium and how these roots adapt to changes in water distribution induced by the presence of structural inhomogeneities in the form of solid intrusions. Physical intrusions such as a square rod added into the 2D granular medium maintain robust capillary action, pumping water from the more saturated areas at the bottom of the cell towards the less saturated areas near the top of the cell while the rest of the medium is slowly devoid of water via evaporation. The intrusion induces “preferential tropism” of roots by first generating a humidity gradient that attracts the root to grow towards it. Then it guides the roots and permits them to grow deeper into more saturated regions in the soil. This further allows more efficient access to available water in the deeper sections of the medium thereby resulting to increased plant lifetime.

Highlights

Interest in water retention has inspired research investigations on water absoprtion and root growth[11,14], with the goal of improving water accessibility and availability for crop productivity[2]
What if we can mechanically induce capillary action, such that water from the deeper and more saturated areas is consistently pumped upwards towards the root zone? This change in water distribution can be generated by modifying the structure of the granular medium by introducing inhomogeneities[14], whose purpose is to redistribute water from the bottom to the top
We investigate experimentally the root growth behavior in response to a change in water distribution induced by the presence of structural inhomogeneities in the granular medium

Summary

Introduction

Interest in water retention has inspired research investigations on water absoprtion and root growth[11,14], with the goal of improving water accessibility and availability for crop productivity[2]. Our choice of inhomogeneity is a solid intrusion, which is inserted in the 2D granular medium This solid intrusion extends throughout the depth of the growth cell, linking the upper portion of the medium near the surface to the fully wet zone at the bottom. We show in these experiments that root elongation can be influenced by the structural inhomogeneities inside the granular medium (“preferential tropism”), thereby inducing a change in water distribution that can significantly control direction and movement of root growth and the subsequent lifetime of a plant. The intrusion further guides the roots towards the deeper parts of the soil

Methods

Results

Conclusion