Root hydraulic properties of spruce measured with the pressure probe

The root pressure probe was used for the first time to measure the hydraulic properties of entire root systems of young Picea abies. Hydraulic conductance was measured by osmotic and hydrostatic pressure relaxation techniques. Osmotic experiments were conducted by changing the nutrient solution and hydrostatic experiments by causing flow across the root with the pressure probe and with external pressure applied to the root system or to the cut stem of the excised root system. Usually, Picea abies root systems did not develop appreciable root pressure (< 0.02 MPA) and could be induced to reach a root pressure of 0.07 MPa by treating with KNO₃. In general, hydraulic conductance of the root system was large, but it was much smaller in the osmotic than in the hydrostatic experiments. Both hydrostatic techniques gave similar results. The results were explainable by a composite transport model of the root.