Seasonal changes in the excess energy dissipation from Photosystem II antennae in overwintering evergreen broad-leaved trees Quercus myrsinaefolia and Machilus thunbergii.

We monitored chlorophyll (Chl) fluorescence, pigment concentration and the de-epoxidation state of the xanthophyll cycle (DPS(1)) in two warm temperate broad-leaved evergreen species (Quercus myrsinaefolia and Machilus thunbergii). Reduction of the maximal quantum yield of Photosystem II (PSII) (calculated from Fv/Fm, variable to maximal Chl a fluorescence) and retention of a high DPS were observed in both species in the winter, and can be interpreted as acclimation to winter. In particular, the acclimation of PSII in these species can be chiefly attributed to thermal dissipation, which is correlated with the retention of high zeaxanthin. Furthermore, we attempted to divide the fate of the absorbed light energy by the PSII antennae into three components: (i) PSII photochemistry (represented by its quantum yield, ΦPSII), (ii) dissipation by down-regulation via non-photochemical quenching (ΦNPQ) and (iii) other non-photochemical processes (ΦONP). The estimated energy allocation of the absorbed light indicated that the proportion of ΦPSII decreased, whereas that of ΦNPQ+ΦONP increased during winter. This result suggests that the excess energy absorbed in the PSII complexes is safely dissipated from the PSII antennae. Based on these results, we conclude that thermal dissipation from the PSII antennae plays an important role in two overwintering broad-leaved evergreen trees growing in Japan.