Effets de températures sub-létales sur l'appareil photosynthétique du chêne vert (Quercus ilex L)

Effects of sub-lethal temperatures on the photosynthetic apparatus of Quercus ilex L. Resistance to high temperatures by the photosynthetic system of leaves of a sclerophyllous tree growing in the Mediterranean basin (Quercus ilex) has been studied using the fluorescence induction technique. Registration of the kinetics with determination of fluorescence decrease ratio was carried out every month for 1 year. According to the dates of sampling, leaves were sorted into 2 categories: > 3 months and < 3 months. They were heated at temperatures of 50, 55 and 60 °C for periods ranging from 0 to 30 min. After sclerification was established (≈ 1 month old) leaves withstood heat with only limited damage at 50 °C. In contrast, the photosynthetic system was totally destroyed when exposed to 60 °C for 30 min. Leaves collected in July displayed some adaptation to high temperatures. The consequences on the functioning of Q ilex in an environment with high temperatures have been examined.