As they push their way through the soil, roots are continuously exposed to mechanical pressure. This often results in their morphological modification. Most obvious are changes in the overall form of the root system as well as in the shapes of particular roots. These changes are often accompanied by modifications of the cell pattern and cell morphology.
Izabela Potocka and Joanna Szymanowska-Pułka focus on the morphological responses of roots to mechanical stress. They examine results of early and recent experiments in which roots have been exposed to mechanical pressure. They review research applying different experimental sets, obstacles, media of various compactness and structure. They also discuss the effect of the combination of mechanical stresses with other abiotic stresses on roots, and results of estimating the force exerted by the roots.
Several modifications in root morphology are commonly reported: (1) decreased root size, (2) radial swelling accompanied by increased radial dimension of the cortex cell layers and (3) enhanced cap cell sloughing. Nevertheless, because of differences between species and individual plants, a universal scenario for root morphological changes resulting from externally applied pressures is not possible. So, knowledge of the root response to mechanical impedance remains a puzzle.
Potocka, I., & Szymanowska-Pułka, J. (2018). Morphological responses of plant roots to mechanical stress. Annals of Botany. https://doi.org/10.1093/aob/mcy010