Abstract: Two-year-old Phoebe zhennan f. elliptical and P. zhennan f. oblong were used to study the photosynthetic pigment content，light response curves，gas exchange，photosynthetic characteristics，and chlorophyll fluorescence parameters in summer. We found that the ratios of chlorophyll a to chlorophyll b （Chl. a/b）in P. zhennan f. elliptical and P. zhennan f. oblong were 2.617 and 2.651，respectively. Therefore，both are shade-requiring plants. The minimal fluorescence（Fo），the actual photochemical efficiency of PSⅡ（ΦPSⅡ），photochemical quenching（qP），and maximum fluorescence（Fm）of P. zhennan f. oblong were higher than those of P. zhennan f. elliptical，although there were no significant differences in the maximum photochemical quantum yield（Fv/Fm）. The light saturation point（LSP）of P. zhennan f. elliptical was higher than that of P. zhennan f. oblong（506.00 vs. 431.00 μmol · m-2 · s-1）. Therefore，P. zhennan f. elliptical has stronger light-utilization ability. However，the light compensation point（LCP）of P. zhennan f. oblong was lower than that of P. zhennan f. elliptical（16.20 vs. 29.25 μmol · m-2 · s-1），which suggests that P. zhennan f. oblong has greater ability to use weak light. The diurnal changes in the net photosynthetic rate（Pn）in summer had a double peak，with the major peak at 10:00 am. The Pn was higher in P. zhennan f. elliptical than in P. zhennan f. oblong（7.52 vs. 5.41 μmol · m-2 · s-1）. The two types of P. zhennan showed a“light lunch break”，which is mainly caused by non-stomatal limitations. In brief，Chl.a/b and LCP were important indicators for measuring shade tolerance. Both types of P. zhennan were shade-requiring plants，although P. zhennan f. oblong had stronger shade tolerance，while P. zhennan f. elliptical can adapt to a wider range of light.

Key words: Phoebe zhennan, photosynthetic characteristics, light response, net photosynthetic rate, chlorophyll fluorescence