Experimental measurement of root growth and root-soil interaction in a bilayered sand using x-ray tomography

While many aspects of the growth mechanisms of plant roots and their ability to adapt to the surrounding environment are now clearer from a biological perspective, relatively limited research has focused on the mechanical interaction of a root and the soil in which it grows, including the root trajectory and the strain developing in the soil. The use of x-ray tomography allows for the 4D (space plus time) analysis of such an interaction. This paper investigates how plant roots grow when approaching a harder-to-penetrate soil – here, a finer and denser sand. The root trajectories in 9 bilayered sand samples are imaged and characterised in terms of their tortuosity. The angle between the root axis and the gravity direction is also measured to characterise the change of trajectory of the root when approaching the stiffer sand layer. Additionally, we report, for one test, the strain path experienced by the soil around the root when the latter is elongating and bending, through imaging conducted at regular intervals during the root growth.