Dissipation mechanisms of excess photon energy under high-temperature stress were studied in a subtropical forest tree seedling, Ficus concinna. Net CO2 assimilation rate decreased to 16% of the control after 20 d high-temperature stress, and thus the absorption of photon energy exceeded the energy required for CO2 assimilation. The efficiency of excitation energy capture by open photosystem II (PSII) reaction centres (Fv′/Fm′) at moderate irradiance, photochemical quenching (qP), and the quantum yield of PSII electron transport (ΦPSII) were significantly lower after high-temperature stress. Nevertheless, non-photochemical quenching (qNP) and energy-dependent quenching (qE) were significantly higher under such conditions. The post-irradiation transient of chlorophyll (Chl) fluorescence significantly increased after the turnoff of the actinic light (AL), and this increase was considerably higher in the 39 °C-grown seedlings than in the 30 °C-grown ones. The increased post-irradiation fluorescence points to enhanced cyclic electron transport around PSI under high growth temperature conditions, thus helping to dissipate excess photon energy non-radiatively. Dissipation mechanisms of excess photon energy under high-temperature stress were studied in a subtropical forest tree seedling, Ficus concinna. Net CO2 assimilation rate decreased to 16% of the control after 20 d high-temperature stress, and thus the absorption of photon energy exceeded the energy required for CO2 assimilation. The efficiency of excitation energy capture by open photosystem II (PSII) reaction centers (Fv ’/ Fm’) at moderate irradiance, photochemical quenching (qP), and the quantum yield of PSII electron transport (ΦPSII) were significantly lower after high-temperature stress. Nevertheless, non-photochemical quenching (qNP) and energy-dependent quenching (qE) were significantly higher than such conditions. The post-irradiation transient of chlorophyll (Chl) fluorescence significantly increased after the turnoff of the actinic light (AL), and this increase was significantly higher in the 39 ° C-grown seedlings than in the 30 ° C-grown ones. The increased post-irradia tion fluorescence points to enhanced cyclic electron transport around PSI under high growth temperature conditions, thus helping to dissipate excess photon energy non-radiatively.