Dissipation of light energy absorbed by photosystem II (PSII) in assimilating shoots of an ever� green shrub Ephedra monosperma was investigated during its transition from the vegetative to frosttolerant state under natural conditions of Central Yakutia. The dynamics of modulated chlorophyll fluorescence and carotenoid content was analyzed during seasonal decrease in ambient temperature. The seasonal cooling was accompanied by a stepwise decrease in photochemical activity of PSII (Fv/Fm = (Fm - F0)/Fm). The decrease in Fv/Fm occurred from the beginning of September to the end of October, when the temperature was lowered from 10 to -8°C. During winter period the residual activity of PSII was retained at about 30% of the summer values. The seasonal decrease in temperature was accompanied by a significant stimulation of pHindepen� dent dissipative processes in reaction centers and antenna of PSII. The increase in energy losses was paral� leled by a proportional increase in zeaxanthin content on the background of decreasing content of violaxan� thin and β�carotene as possible zeaxanthin precursors. At the same time, inhibition of lightinduced non� photochemical quenching in the PSII antenna was observed. The results suggest that principal photoprotec� tive mechanisms during seasonal lowering of temperature are: (1) inactivation of PSII and dissipation of exci� tation energy in PSII reaction centers and (2) zeaxanthinmediated ener gy dissipation in the antenna com� plexes. The first mechanism seems to prevail at early stages of seasonal cooling, whereas both mechanisms are recruited from the onset of sustained freezing temperatures.