Saugspannungsdiagramm für austrocknende Blätter von Quercus ilex L.

Abstract

Summary Suction tension (depression of water potential) and osmotic pressure of young and mature sclerophyllous leaves of Quercus ilex were determined during desiccation until drought injuries occurred. The suction tension was measured with the Wescor Sample Chamber Psychrometer, the osmotic pressure by cryoscopy; from measured values of the osmotic pressure and the suction tension the turgor pressure was calculated. In leaves of Quercus ilex the suction tension does not fall to zero when the twigs are saturated with water, but remains at a level of about 4 bar (young leaves) to 9 bar (mature leaves). At water saturation deficits between the point of turgor loss and the appearance of the first drought injuries, the suction tension rises above the level of the osmotic pressure, thus indicating the effectiveness of negative turgor pressure. The higher the drought resistance of the leaves, the higher the values of negative turgor pressure and suction tension achieved.