Abstract: To explore the influences of soaking time and applied concentration of GA₃ on seed germination of Astragalus membranaceus under severe drought and salt stresses, five concentrations (0, 50, 100, 200 and 400 mg·L^-1) of GA₃ were used to soak seed separately in five duration periods (6, 12, 24, 36 and 48 h), and then treated seeds were transferred to -0.6 MPa PEG and -0.9 MPa NaCl solutions to conduct experiment, with total germination percentage and mean germination time being measured. With the extension of soaking time and increased GA₃ concentration, total germination percentage of A. membranaceuswere enhanced under both stresses, and the differences were significant among treatments (P<0.05). Under NaCl stress, the highest total germination percentage was 83.33%, which occurred in treatment of soaking seeds for 36 h with 100 mg·L^-1 GA₃. Under PEG stress, the highest total germination percentage was 80.00% which occurred in treatment of soaking seeds for 48 h with 100 mg·L^-1 GA₃. Total germination percentages were suppressed in high concentrations (more than 200 mg·L^-1) of GA₃ over 24 h. Changing seed coat’s permeability and enhancing embryo viability may be the key factors under GA₃ soaking treatments, which effectively promoted seed germination. Results simulated by Design Expert software indicated that 100 mg·L^-1 GA₃ with soaking seeds for 36 h would be an optimum treatment for germination under integrated severe osmotic stress.

Key words: Phoebe bournei, photosynthetic characteristics., chlorophyll content, shading