Abstract：
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Cuttings of Populus kangdingensis C. Wang et Tung and Populus cathayana Rehder, originating from high and low altitudes in the eastern Himalaya, respectively, were examined during one growing season in a greenhouse to determine the effects of progressive drought stress. The results manifested that the adaptiveponses to progressive drought stress were different in these two pecies from different altitudes. Significant changes in stem height, af development, relative water content (RWC), malondialdehyde (MDA) and hydrogen peroxide (H2O2) appeared earlier in P. cathayana than in P. kangdingensis, whereas changes in soluble protein,
soluble sugar, free proline and antioxidant enzymes appeared earlier in P. kangdingensis. In addition, changes in these parameters became more and more significant when the drought
stress progressed, especially under severe drought stress in P. cathayana. Plant growth showed significant positive correlations with soluble proteins and sugars, free proline and antioxidants
and a significant negative correlation with RWC under water stressed treatment in two poplar species. Compared with P. cathayana, P. kangdingensis was able to maintain a superior
height growth and leaf development under drought stress. Also, P. kangdingensis possessed greater increments in soluble protein, soluble sugar, free proline and antioxidant enzymes, but
lower increments in MDA and H2O2 than did P. cathayana when the cuttings were exposed to progressive drought stress. Our results suggest that P. kangdingensis originating from the high altitude has a better drought tolerance than does P. cathayana iginating from the low altitude. Furthermore, this study manifested that acclimation to drought stress are related the rapidity, severity, duration of the drought event and the altitude of two poplar species.
