The effects of temperature on root and shoot hydraulic conductances (g(shoot) 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) increased considerably with temperature from 0-50 degrees C. Between 15 degrees C and 35 degrees C, g(shoot) and g(root) varied with water viscosity. In a second experiment, the impact of temperature-induced changes in g(root) on sapling transpiration (E) and leaf water potential (psileaf) was assessed. Intact plants were placed in a growth cabinet with constant air and variable soil temperatures. E increased linearly with soil temperature but psileaf remained constant. As a consequence, a linear relationship was found between 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.
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Cochard et al. (2000) studied this question.