Abstract: The hybrid poplar is the important garden and afforestation tree species on Songnen Plain saline-alkali land, long-term field monitoring is the key to evaluate and optimize superior varieties. Under the natural conditions, different four-year-old cutting seedlings of Qing Shan Yang (Populus Pseudo-cathayana×P. deltodides cv. Shan Hai Guan), Xiao Hei 14 (Populus×xiao hei T.S. Hwang et Liang ‘14’) and Zhong Hei Fang (Populus deltoids×P. cathayana) that grew at different saline-alkali land in Daqing City were used as the research (study) materials. Through the comparison and analysis of the growth (height and basal diameter), root activity, root respiration and chlorophyll content, the growth adaptability and salinity tolerance differences in the saline-alkali soil were explored. The results show that, with the saline-alkali stress(soil electrical conductivity from 609.33 μs·cm^-1 to 910.48 μs·cm^-1 and pH from 8.92 to 8.98) enhanced, the growth of hybrid poplar was restrained obviously,the tree heights of Qing Shan Yang merely declined 20%,only one half of that for Zhong Hei Fang and Xiao Hei 14.With the saline-alkali stress enhanced, root activity and root respiration were enhanced, the root activity of Qing Shan Yang, Zhong Hei Fang and Xiao Hei 14 improved 10.75%,15.90%and 33.17% respectively, root respiration of Qing Shan Yang merely increased 3.59%, that of the other two varieties increased more than 24%.However, in saline-alkali stress the chlorophyll content was less affected, the annual mean was decreased slightly，Chla/b ratio was increased, smaller differences existed between different species. Comprehensive researches of various indices of three hybrid poplars,the ability of tollerance to saline-alkali stress of Qing Shan Yang is stronger than the other two. The growth of Qing Shan Yang is obviously better than Zhong Hei Fang and Xiao Hei 14, which were generally applied on saline-alkali land at present. Comparatively speaking,Qing Shan Yang is an improved hybrid poplar variety for afforestation and greening on saline-alkali land.

Key words: Hybrid poplars, saline and alkaline, growth status, chlorophyll, root vitality