VULNERABILITY TO AIR-EMBOLISM OF 3 EUROPEAN OAK SPECIES (QUERCUS-PETRAEA (MATT) LIEBL, QUERCUS-PUBESCENS WILLD, QUERCUS-ROBUR L)

The vulnerability to water-stress induced cavitation and the petiole leaf specific conductivity (LSC) have been studied on excised branches of Quercus petraea, Q pubescens, Q robur and Q rubra. Seasonal evolution of xylem embolism in the petioles and twigs of mature Q petraea has been followed together with increasing soil water deficit. Field experiments showed that Q petraea suffered from embolism damage in both petioles and twigs after heavy drought. Large differences in terms of vulnerability to cavitation and LSC have been found between species. Q pubescens presented the highest LSC and the lowest vulnerability together with Q petraea. Q robur was found to be more vulnerable than Q petraea although with comparable LSC. Q rubra was the most vulnerable species and exhibited the lowest LSC. It was concluded that these species could be classified according to how their hydraulic mechanism is conceived to resist cavitation events : Q pubescens was the most resistant followed in order by 0 petraea, Q robur, and Q rubra. Results are discussed in terms of plant segmentation and drought resistance.