Abstract: In this study,the effects of simulated water (PEG-6000) and salt (NaCl) stresses on seed germination of Gymnocarpos przewalskii were analyzed so as to determine its drought and salt tolerance by designing the osmotic potentials of -0.3,-0.5,-0.7,-0.9 and -1.2 MPa and distilled water as control (0 MPa).The result showed that the seed germination of G.przewalskii was inhibited significantly by the two stresses.PEG stress reduced significantly the seed germination index,vigor index and radicle length.When the osmotic potential was ≤-0.7 MPa,the germination rate was significantly decreased.Germination index and radicle length were decreased significantly under NaCl stress.When the osmotic potential was ≤-0.9 MPa,the germination rate was significantly reduced.Germination index,vigor index and radicle length were sensitive to salt and water stresses and could be used as the main indexes to evaluate the drought and salt tolerance of G.przewalskii seeds.Under iso-osmotic condition,when the osmotic potentials were -0.7 MPa and -0.9 MPa,the germination rate,vigor index and hypocotyl length of PEG stress were significantly lower than those of NaCl stress; when the osmotic potential was ≤-0.7 MPa,the germination potential and germination index under PEG treatment were significantly lower than those under NaCl treatment,which indicated that the main factors affecting seed germination was osmotic stress rather than ionic toxicity.The critical and limit values of seed germination were -0.8 MPa and -1.1 MPa respectively under PEG stress,and they were -1.5 MPa and -2.2 MPa under NaCl stress.Which indicated that the salt tolerance of seed germination of G.przewalskii was higher than drought tolerance.

Key words: Gymnocarpos przewalskii, iso-osmotic condition, NaCl stress, PEG stress, seed germination, Anxi