Abstract
Roots provide basic functions to plants such as water and nutrient uptake and anchoring in soil. The growth and development of root systems contribute to colonizing the surrounding soil and optimizing the access to resources. It is generally known that the variability of plant root architecture results from the combination of genetic, physiological, and environmental factors, in particular soil mechanical resistance. However, this last factor has never been investigated at the soil grain scale for roots. In this paper, we are interested in the effect of the disordered texture of granular soils on the evolution of forces experienced by the root cap during its growth. We introduce a numerical model in which the root is modeled as a flexible self-elongating tube that probes a soil composed of solid particles. By means of extensive simulations, we show that the forces exerted on the root cap reflect interparticle force chains. Our simulations also show that the mean force declines exponentially with root flexibility, the highest force corresponding to the soil hardness. Furthermore, we find that this functional dependence is characterized by a single dimensionless parameter that combines granular structure and root bending stiffness. This finding will be useful to further address the biological issues of mechanosensing and thigmomorphogenesis in plant roots.
Highlights
The plant-root system displays two main functions essential for plant growth, which are mechanical anchoring and water and nutrient uptake [1,2]
In this paper we introduced a simple discrete numerical model of root growth inside a granular soil
The root development is guided by the disordered texture of the granular medium and the reaction forces exerted by the particles on the meristem, modeled here as the growing segment of the root. We found that these forces are well above the mean particle weight almost independently of the depth, and their statistical distribution reflects that of interparticle forces with an exponentially decaying number of strong forces
Summary
The plant-root system displays two main functions essential for plant growth, which are mechanical anchoring and water and nutrient uptake [1,2]. We investigate the distribution and evolution of forces exerted by soil grains on a root modeled as a self-elongating elastic tube of constant thickness Active apex movements such as gravitropism or other deviations due to anisotropic cell growth are not considered here, i.e., the root path is only driven by external forces exerted by the surrounding grains. This choice was made in order to dissociate the external mechanical component from the biological component of root trajectory. VI with a summary of the main findings of this work and a brief discussion of its possible extensions
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