Root-soil contact dynamics of Vicia faba in sand

Root shrinkage in drying soil has been shown repeatedly. The aim of this study was to investigate the dynamics of root-soil contact and its relationship with plant water status during soil drying. The development of root-soil contact of Vicia faba L. during a drying period was studied. Plants (N = 4) were grown in cylinders filled with a sandy soil. Samples were repeatedly scanned with an X-ray CT scanner to visualize root-soil contact. Soil matric potential, transpiration rate, and stomatal conductance were measured daily. Root-soil contact was lower in taproots than in lateral roots at any time. Transpiration rate and stomatal conductance decreased before roots started to shrink. Root-soil contact decreased significantly over the course of the drying period, starting at soil matric potentials below -20 kPa. Root shrinkage did not differ significantly between taproots and laterals. This study confirms previous findings with Lupinus albus roots in that roots shrink after transpiration rate decreases. The dynamics of root shrinkage are governed by soil water availability and transpirational demand.