Abstract: Selenium is a necessary element for plant growth. This study employed the method of pot experiments to investigate the effect of exogenous selenium concentration on the growth of annual seedlings and chlorophyll fluorescence parameters of Apocynum venetum L. The results showed that annual A. venetum L. seedling growth and chlorophyll fluorescence parameters had significant correlation under root applied Selenium (R) or spray Selenium of A. venetum L. Within a certain range of concentration （0-1.5 mg·kg^-1），stem dry weight，weight，plant height，stem diameter，the number of leaves of A. venetum L. on the stem and branches increased significantly with the increase of selenium concentration. Fv/Fm，Fv/Fo，Ψo，φEo，PIABS also increased with the increase of selenium concentrations while V_K，V_J，V_I gradually decreased. However，the growth and chlorophyll fluorescence parameters of Apocynum venetum L. reduced with the excessive supply of selenium. Selenium promoted the growth of Apocynum，particularly the function of the root system，which reinforced the nutrient absorption ability of the plant. Although high concentration （3-5 mg·kg^-1） of selenium put stresses on the aboveground parts of the plant，it could still boost the growth of the root. There might be two reasons why the root can grow fast under the high concentration. On the one hand，the root might have a better tolerance to selenium toxicity than the rest parts of the plant. On the other hand，it was possible that A. venetum L. had had developed an adaptive response to selenium poisoning. A. venetum L. could change the growth strategy to let more photosynthetic product and nutrients being allocated to roots，to increase root cap ratio and to improve the absorbing ability to maintain the normal growth. A certain concentration of selenium can improve the activity of PSII and increase the PSII reaction central open degree，and then improve the utilization rate of light energy，so as to effectively promote the growth of A. venetum L.. The suitability range of selenium concentration was not obvious. The concentration below 1 mg·kg^-1 had no significant influence on the growth of A. venetum L. but the concentration greater than 3 mg·kg^-1 would significantly inhibit the growth of the plant. Therefore，concentration of selenium should be strictly controlled within 1-3 mg·kg^-1 to avoid the accumulation of selenium in the soil. Leaf spray might be a better harmless way to improve the growth of the plant.

Key words: Apocynum venetum L., Selenium, chlorophyll fluorescence