SUMMARY

The vulnerability to cavitation-induced xylem embolism of three Mediterranean sclerophyllous trees, namely Ceratonia siliqua L., Olea oleaster Hoffmgg et Link and Laurus nobilis L. was investigated as a major factor in their overall drought resistance. Also the capability of the three species of recovering from xylem embolism was studied. C. siliqua and O. oleaster plants suffered only minor damage to the hydraulic conductivity of their young twigs, under water stress conditions simulating those recorded in the field in May and September in Sicily and in September in Turkey. L. nobilis plants, on the contrary, appeared not only to be much more vulnerable to xylem embolism but they were also not capable of repairing damage to xylem water conductivity within 24 h of rewatering. This may explain why leaf water potential remained much more negative than xylem water potential in rewatered Laurel plants, because xylem embolism in leaf petioles prevented water being transported to leaves. The analysis of the distribution of xylem conduit diameter in the leaf petioles of the three species, showed that L. nobilis petioles had wider xylem conduits than the other two species. In this comparison, wider xylem conduits appear to be more vulnerable to cavitation than narrower ones. The major vulnerability of L nobilis to cavitation is related to the different distribution of this species with respect to C. siliqua and O. oleaster within the Mediterranean basin region.