Abstract:Photosynthetic rates and chlorophyll a fluorescence were measured with a photosynthetic measurement system (Li-Cor 6400) and leaf chamber fluorometer (Li-Cor6400 LCF) in leaves of saplings of the sun-adapted species (Schima superba),shade-adapted species (Cryptocarya concinna) and the mesophytic plant (Castanopsis hystrix) during the exposition to moderate high-temperature stress (42℃). The results showed that moderate high-temperature stress led to a decrease in Fv/Fm, namely the primary photochemical quantum efficiency, indicating that moderate high-temperature stress causes a partial inhibition of PSII. It also showed that such an effect was more severe in the shade plant C. concinna than in the sun-adapted species S. superba. Nevertheless, except for the sun-grown leaves of C. concinna, the moderate high-temperature stress increased the photosynthetic rate of leaves at high light intensity. Simultaneously, less photo-inhibition was found to occur under high-light intensity, suggesting that the capacity of resistant-photoinhibition was stimulated by moderate high-temperature stress. The quantum yield of PSII (ΦPSII) decreased in sun-grown leaves of S. superba and C. hystrix, but did not significantly change in leaves of the shade plant C. concinna and shade-grown leaves of sun plant S. superba or the mesophytic plant C. hystrix because they had already a very low ΦPSII under this condition. Moderate high-temperature stress led to a decrease in ΦPSII/ΦCO2 ratios, an estimate of the quantum requirement, in the sun plant S. superba and the mesophytic plant C. hystrix, since they were associated with a lower fraction of excitation energy dissipated. However, no significant changes were found in shade plant C. concinna and in shade-grown leaves of the other examined plants. The effects of moderate high-temperature (42℃) on photosynthesis depends on species and leaf type (sun and shade leaves) of the saplings of subtropical broad-leaf trees.