Hydraulic Properties of Pine and Bean Roots With Varying Degrees of Suberization, Vascular Differentiation and Mycorrhizal Infection.

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Abstract
The hydraulic behaviour of root systems of loblolly pine seedlings conformed to the model of Fiscus (1975) and Dalton et al. (1975). The average hydraulic conductance per unit of root surface area was 1.4 × 10-6 cm s-1 bar-1. The hydraulic conductance of various parts of pine root systems was determined using root severing experiments. The average hydraulic conductance of brown (older suberized) roots was 7.55 × 10-7 cm s-1 bar-1, and that of white (newly regenerated unsuberized) roots was 1.95 x 10-6 cm s-1 bar-1. Hydraulic conductance was independent of the amount of mycorrhizal infection. The mean maximum exudation rate from detopped seedlings at zero hydrostatic pressure difference was 1.31 × 10-7 cm s-1. Axial conductance of nutrient solution by roots of bean plants and loblolly pine seedlings was measured at 25°C. Bean vessels and pine tracheids conducted at 0.4 and 0.55 times idealized Poiseuille conductance. Bean roots with differentiated vessels had 8 times more axial conductance per unit area of stele than pine roots, and 6.5 times more axial conductance than bean roots with undifferentiated vessels. Change in axial conductance of bean roots with temperature was completely explained by change in viscosity of the solution. Axial resistance was negligible in the experiments where the hydraulic conductance of whole root systems was measured.