Abstract: A field research was conducted on the characteristics of chlorophyll fluorescent parameters and daily dynamics of photosynthesis in dioecious Populus cathayana cutting seedlings. The results showed as follows: The curves of diurnal variation in P_n, T_r and G_s of dioecious cutting seedlings leaves had two peaks, and a significant midday depression phenomenon, although there were differences in the time and the value of the peaks and valleys occurred in terms of P_n, T_r and G_s. WUE_i decreased from morning to noon, reached the lowest value and then increase, he female individuals had the highest value of WUE_i at 16:00; The photosynthetic indexes of male individuals such as P_n, G_s, T_r, WUE_i, F_m, F_o, F_m′, F_o′, F_v′/F_m′ and ETR were significantly higher than those of female individuals (P<0.05), but significantly lower NPQ than female individuals. Moreover, the gender-pecific differences of male and female cutting seedlings in C_i, L_s, F_v/F_m, F_v/F_o, Ф_PSⅡ and qP were not significant (P> 0.05); Correlation analyses showed that the parameters affecting P_n could be ranked, from the highest to the lowest, as G_s>C_a>RH>VPD>T_a>PAR, and the factors T_r could be ranked as G_s>C_a>RH>VPD>PAR>T_a. The effects of climate factors on photosynthesis rate, transpiration rate of P.cathayana were obvious. Comparing with the female, the male had higher efficiency of light energy captured, electron transport rate, photosynthetic efficiency and water use efficiency, and thus, had greater resistance against adversity.

Key words: Populus cathayana, dioecious, photosynthetic rate, chlorophyll fluorescence, environmental factor