Leaf senescence is a complex phenomenon occurring in all plant species,but it is still poorly understood in plants grown in Mediterranean field conditions and well-adapted to harsh climatic conditions.To better understand the physiological processes underlying leaf senescence in mastic trees (Pistacia lentiscus L.),we evaluated leaf growth,water and N content,photosystem Ⅱ (PSⅡ) photochemistry,lipid peroxidation and levels of photosynthetic pigments,antioxidants,abscisic acid,and salicylic acid and jasmonic acid during the complete leaf lifespan,from early expansion to late senescence in relation to natural climatic conditions in the field.While mature leaves suffered from water and N deficit during late spring and summer,both young (emerging) and old (senescing) leaves were most sensitive to photooxidative stress,as indicated by reductions in the Fv/Fm ratio and enhanced lipid peroxidation during late autumn and winter.Reductions in the Fv/Fm ratio were associated with low α-tocopherol (vitamin E) levels,while very old,senescing leaves additionally showed severe anthocyanin losses.We have concluded that both young (emerging) and old (senescing) leaves suffer oxidative stress in mastic trees,which may be linked in part to suboptimal temperatures during late autumn and winter as well as to low vitamin E levels.