Abstract: Two-year-old red pine seedlings were grown in soils to study the effects of different water treatments (including aridity and waterlogging stress) and relief stress on the plasma membrane permeability and protective enzyme activities of red pine seedling needles. The main results were as follows: with the time extension of aridity and waterlogging stress, the contents of proline, soluble sugar and malondialdehyde (MDA) increased; the activities of catalase (CAT) decreased; and the peroxidase (POD) activities rose. After relief stress, the tested indices of all treatments experienced different levels of recovery. Among them, the tested indices of FC40%, FC80% and FC restored relatively fast. However, indices of FC20% and FL could not completely recover within 14 days. Moreover, FL had the worst physiological performance. To sum up, 60% was the optimum soil water content to red pine seedlings, because the seedlings under this circumstance presented the most comprehensive physiological performance.

Key words: Red pine(Pinus resinosa Ait.), water stress, relief stress, plasma membrane permeability, membrane lipid peroxidation, osmoregulation