Bio-mechanics and plant root growth

[\Plant or tree roots adapt their morphology according to the mechanical and topological properties of the soil. Depending on the soil density or confining pressure, on the size and connectivity of pores between solid constituents of the soil, the root will be blocked or grow further, either by curving and avoiding obstacles or by pushing the grains forming the soil./]

Growth of a Chick-pea root in an elastomeric tube. Deflection of a Chick-pea root under increasing loads.

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As soil strength increases, it is usually observed that root elongation rate decreases and that the root thickens radially instead of elongating longitudinally. Therefore the competing effects of soil mechanical impedance and penetrating capacities of the plant lead to different strategies for root development, whose growth in turn modifies the soil physical properties. It is therefore of primary importance to design simple conceptual experiments to understand progressively the intricate soil/root system from a mechanical point of view.

Our objective is therefore to study the coupling and retroaction between the root growth and the reorganization of a granular soil , i.e. what are the forces a root is able to develop on the surrounding grains and how the mechanical stress due to this environment affects the root growth (morphogenesis) at the macroscopic and tissular levels./]

Growth of a Chick-pea root through a pore between two photoelastic discs placed between circular polarizers. The evolution of the black fringe pattern is a way to measure the force exerted by the root during its growth.