Chilling-induced photoinhibition in two oak species: Are evergreen leaves inherently better protected than deciduous leaves?

We compared the sensitivity to cold stress, in terms of photosynthetic capa city and changes in chlorophyll fluorescence of photosystem 2 (PS2), of an evergreen and a deciduous oak species, which co-occur in the southeastern U nited States. We predicted that the evergreen species, Quercus virginiana, which must endure winter, is likely to have an inherently greater capacity for energy dissipation and to be less susceptible to chilling stress than t he deciduous species, Quercus michauxii. Shortterm cold stress in both spec ies lead to greater than 50 % reduction in maximum photosynthetic rates, 60 -70% reduction in electron transport, and irreversible quenching of PS2 flu orescence. The kinetics of recovery in the dark after exposure to 1 h high irradiance (1000 mu mol m(-2) s(-1)) and chilling (5 degrees C) showed that the evergreen Q. virginiana exhibited more protective q(E) and less irreve rsible quenching (q(I)) than the deciduous Q. michauxii. The large q(E) whi ch we observed in Q. virginiana suggests that the capacity for photoprotect ion at low temperatures is not induced by a long-term acclimation to cold b ur preexists in evergreen leaves. This capacity may contribute to the abili ty of this species to maintain leaves during the winter.