ROOT HYDRAULIC-PROPERTIES OF SPRUCE MEASURED WITH THE PRESSURE PROBE

The root pressure probe was used for the first time to measure the hyd raulic properties of entire root systems of young Picea abies. Hydraul ic conductance was measured by osmotic and hydrostatic pressure relaxa tion techniques. Osmotic experiments were conducted by changing the nu trient solution and hydrostatic experiments by causing flow across the root with the pressure probe and with external pressure applied to th e 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 sys tem was large, but it was much smaller in the osmotic than in the hydr ostatic experiments. Both hydrostatic techniques gave similar results. The results were explainable by a composite transport model of the ro ot.