Abstract: Aimed to examine the adaptability of Qingshan poplar (Populus pseudo-cathayana × P. deltoides) to salt-alkali stress, two-year-old cutting seedlings of the poplar were treated with 28 combinations of salt-alkali stress. With increasing salt concentration, the leaf electrolyte leakage and MDA and proline contents of test seedlings all showed an increasing trend, while the leaf soluble sugar content and SOD and POD activities increased first but decreased afterwards. The increase of substrate pH made the electrolyte leakage, MDA content, and POD activity increased and the proline and soluble sugar contents decreased after an initial increase, but had lesser effects on the SOD activity. When the salinity was < 100 mmol·L-1 and the pH was increasing, all test physiological indices had a slight change while SOD activity kept at a higher level; when the salinity was > 200 mmol·L-1 and the pH was higher than 8.99, the electrolyte leakage was higher than 50%, POD activity and MDA content increased obviously, proline and soluble sugar contents declined, and SOD activity was lower. It was concluded that a salt-alkali condition with salinity > 200 mmol·L-1 and pH >899 was not appropriate to the growth of Qingshan poplar.

Key words: Qingshan poplar, salt-alkali stress, osmoregulation substance, active oxygen metabolism, river ecosystem, ecological function evaluation, management strategy, Taizi River.