Responses of Quercus ilex from different provenances to experimentally imposed water stress

Responses of Quercus ilex L. seedlings from three different localities in Italy to experimentally imposed drought stress were analysed. Predawn (Ψpd) and midday (Ψm) leaf water potential of stressed seedlings decreased on an average until -4.0 and -4.2 MPa, respectively, in the severe water stress. At the end of the severe water stress the relative water content (RWC) was 72.5-83.6% and the photosynthetic rates (PN) near zero. The critical threshold value of Ψpd for complete stomatal closure was from -4.0 to -4.5 MPa. The leaf damage after the severe water stress was significantly greater in seedlings originated from the acorns of climax area (45% total leaf injured area and 40% fallen leaves) than in the other seedlings (on an average 20.5% total leaf injured area and 21% fallen leaves).