Temperature effects on hydraulic conductance and water relations of Quercus robur L.

The effects of temperature on root and shoot hydraulic conductances (g(shoo t) and g(root)) were investigated for Quercus robur L. saplings. In a first experiment, conductances were measured with a High Pressure Flow Meter on excised shoots and detopped root systems. The g(root) and g(shoot) increase d considerably with temperature from 0-50 degrees C. Between 15 degrees C a nd 35 degrees C, g(shoot) and g(root) varied with water viscosity, In a sec ond experiment, the impact of temperature-induced changes in g(root) on sap ling transpiration (E) and leaf water potential (Psi(leaf)) was assessed. I ntact plants were placed in a growth cabinet with constant air and variable soil temperatures, E increased linearly with soil temperature but Psi(leaf ) remained constant. As a consequence, a linear relationship was found betw een E and g(plant), The results illustrate the significance of g(plant) for the stomatal control of transpiration and the significance of temperature for tree water transport.