Root growth response to rigid obstacles.

In the current context of climate change and the ensuing hardening of the soil because of a predicted increase of drought events, studying the effect of soil mechanical resistance on growing roots takes a whole new significance and importance. Our research aims at studying the impact of mechanical stress on a primary root growing inside a soft homogeneous soil and encountering a single rigid obstacle such as a stone or a hard pan.

To mimic such a system, maize seedlings were grown inside a soft gel (agarose gel 2% w/w) placed above a force sensor acting as an obstacle. The root was guided through a vertical cylindrical hole pre-formed inside the gel. The whole setup was illuminated with Infra-Red lighting, to perform time-lapse imaging of the root growth as well as detailed kinematic studies of the root growth zone through a PIV technique. Growth observation was coupled with force measurements when the root tip emerged from the gel and pushed against the force sensor.

Force-velocity relationships and strain rate profiles along the root axis were established to test the validity of Lockhart-type growth models under mechanical stress.