Abstract: [Objective] This study investigated the growth and physiological adaption of the growth process of Populus×euramericana in different irradiation duration, in order to provide a theoretical basis for the early breeding and promotion of the superior varieties with high photosynthetic efficiency.[Method] In this paper, seedlings of 16 P.×euramericana clones were taken as experimental materials, and artificial light control tests were performed with LED-100W full spectrum plant growth lamp under all shading conditions to study the influence of different irradiation duration (11 h, 12 h, 13 h, 14 h and 15 h) on the seedlings growth, the biomass, the relative content of chlorophyll and the photosynthetic characteristics of P.×euramericana. [Result] 1)The results showed that relative growth rate of height and root diameter, and leaf biomass of seedlings under 14 h and 15 h irradiation were significantly higher than those under other irradiation duration (P<0.01). On the contrary, the root-shoot ratio and leaf SPAD value were relatively low. The trends of light-response curves of seedlings under different irradiation duration were basically consistent. With the increase of photosynthetically active radiation (PAR), the net photosynthetic rate (P_n) of leaves increased rapidly at first, and then began to flatten after reaching the light saturation point. The rectangular hyperbola was a favorable model for fitting the light-response curve data (R²≥0.948). 2)The maximum net photosynthetic rate (P_max) of leaves increased as the light time prolonged, and was 104.53% higher with 15 h irradiation than that with 11 h irradiation. Apparent quantum yield (AQY), dark respiration (R_d), and light compensation point (LCP) were the highest with 15 h irradiation. Light saturation point (LSP) was relatively higher under 14 h irradiation, with only lower than 13 h irradiation, while LCP and R_d were lower than all the other irradiation duration. 3) The chlorophyll fluorescence parameters showed that basis fluorescence (F_o) of seedlings under 11 h irradiation was the highest, and the maximum fluorescence (F_m) was not significantly different (P>0.01). Variable fluorescence (F_v) of seedlings under 13 h irradiation was relatively higher. The efficiency of solar energy conversion (F_v /F_m) and potential activity of PSⅡ(F_v /F_o) increased gradually with the increase of irradiation time, and the value of (F_v /F_m) ranged from 0.83 to 0.85.[Conclusion] Within the scope of this study, as the extension of light time, the P_max、F_m、F_v、F_v/F_o and F_v/F_m of P.×euramericana seedlings increased gradually, while F_o and root-shoot ratio decreased gradually. Besides, SPAD value, AQY, LSP, LCP, and R_d also had different responses to irradiation duration. Therefore, we suggest that the results can be used as an indicator of the early growth and the ecological adaption of P.×euramericana seedlings, also can be used as an important reference of the new varieties breeding, the application of breeding varieties and production practices.

Key words: light time, Populus×euramericana, growth, photosynthesis, fluorescence characteristics