Abstract:The gas exchange feature and chlorophyll fluorescence parameters in seedlings of three endangered Magnoliatia species (M. aromatica, M. megaphylla and M. grandis.) were determined by LI-6400 portable photosynthesis analysis system (LI-6400, Li-cor USA), leaf disc oxygen electrode (Hansatch, King′s Lynn UK) and chlorophyll fluorometer (Maxi-Imaging-Pam, Walz, Germany) in summer. The results showed that the diurnal variation of net photosynthetic rate in leaves of three plants presented a two-peak curve pattern. The first peak and second peak occurred at about 08:00 and at 14:00-16:00, respectively. An obvious phenomenon of “midday depression of photosynthesis” was observed at noon. Maximum photosynthetic rates (Pmax) were 5.2-7.4μmolm-2s-1, light compensation points (LCP) for photosynthesis were 14-17 μmol m-2s-1, and the light saturation intensities (LSP) were 500-800μmolm-2s-1 in leaves of three Magnoliatia plants. The Pmax, LSP and apparent quantum yield (AQY) of M. megaphylla were significantly higher than that of the other two plants. Under saturated CO2 concentration , the oxygen evolution rate increased firstly with increasing temperature and decreased thereafter. the optimal temperature were around 35℃ in three plants of Magnoliatia. Leaves of M. aromatica showed an obviously lower oxygen evolution rate as compared with that in M. megaphylla and M. grandis, When leaves were suffered to a short term of high temperature treatment (45-50℃), the maximal photochemical efficiency of photosystem Ⅱ (Fv/Fm) decreased obviously, while the minimal fluorescence (F0) increased. The changing extent in M. megaphylla was less than that in M. aromatica and M. grandis. Hence, the sequence of photosynthetic rate and tolerance to high temperature in three Magnoliatia plants from high to low is suggested to be M. megaphylla＞M. grandis＞M. aromatica.