VULNERABILITY TO FREEZE STRESS OF SEEDLINGS OF QUERCUS-ILEX L - AN ECOLOGICAL INTERPRETATION

The vulnerability to freeze stress of seedlings of Quercus ilex L. was studied with the aim of defining the limits of the potential distribu tion area of this species in its northernmost habitat. In December 199 6 seedlings were freeze stressed up to -8 degrees C for 3 d. Frost cau sed extensive functional damage to seedlings in terms of: a) leaf wate r status; b) root (K-r) and stem (K-s) hydraulic conductance; c) tissu e disorder in the root (only nine seedlings out of 50 survived). In co mparison with unstressed seedlings, K-r and K-s of freeze-stressed see dlings were reduced by 90 %. Root anatomy of freeze-stressed seedlings revealed that: a) cortex cells were dehydrated and had become separat ed from one another; b) the endodermis was oversuberized, thus isolati ng the stele from the cortex. Our conclusion was that Q. ilex is extre mely vulnerable to freeze stress so that the distribution area of the species is restricted to zones with no frost events. ((C) Inra/Elsevie r, Paris).