Abstract: We investigated the effects of temperature on seed germination and seedling growth of two Astragalus species (A. mongholicus and A. complanatus) under drought and salt stresses. Purified water treatment was regarded as control group. The treatments of NaCl and PEG  were set up, with four osmotic potential levels (0, -0.1, -0.3, -0.5 MPa). Seeds were cultured under five different temperatures (10, 15, 20, 25 and 30 ℃), respectively. Seed germination and seedling growth were observed and recorded every day. The results showed that the optimum temperature for germination of A. mongholicus and A. complanatus under stresses were about 25 and 20 ℃, respectively. A. mongholicus was resistant to high temperature, while A. complanatusshowed the opposite. Both 25 and 20 ℃ were suitable for seedling growth of both species, asindicated by the growth of radicle, hypocotyl and cotyledon. The mean germination time of A. mongholicus in each treatment group (except ungerminated seeds) was longer than that of A. complanatus. With the increases of NaCl stress, total germination percentage of both species seeds reduced, with higher salt tolerance of A. mongholicus. With increasing PEG stress, seed germination of both species was inhibited, even without any germination. However, the drought tolerance of A. complanatuswas higher than that of A. mongholicus. Under the same osmotic potential, PEG showed a stronger effect than that of NaCl, especially at -0.5 MPa. Under combined stresses, seedling growth (such as the fresh and dry weight, the length of radicle and hypocotyl, and the length and width of cotyledon) of both species varied greatly with increasing osmotic potential. Design Expert software predicted that 25 ℃ with -0.1 MPa NaCl treatment and 24 ℃ with -0.04 MPa PEG treatment were the optimum combinations for seed germination and seedling growth ofA. mongholicus, while the optimum combination for A. complanatus were -0.07 MPa NaCl treatments at 23 ℃ and -0.13 MPa PEG treatments at 20 ℃.

Key words: temperature, drought, salt, interaction stress, seed germination, seedling growth.