[Responses of seed germination of Astragalus membranaceus to light and temperature conditions accompanied with drought and salt stresses]

We studied the seed germination of Astragalus membranaceus under PEG and Na Cl osmotic stress gradients( 0,-0. 1,-0. 3,-0. 5,-0. 7 MPa) respectively applied with light( continuous light,light 12 h/dark 12 h circulation and continuous dark) and temperature( constant 15 ℃,15 ℃ 12 h/30 ℃ 12 h circulation and constant 30 ℃) treatments. The results showed as following: ① Under the light and temperature interactive treatments,total germination percentage( TGP) was restrained by high temperature and continuous light also decreased TGP under high temperature. Mean germination time( MGT) was not changed by light mode. Root development was enhanced by dark and low temperature. Shoot development was enhanced by light and high temperature. Hypocotyl length was enhanced by dark and high temperature. ② Under the light and temperature interactive treatments combined respectively with PEG and NaCl stress conditions,although the inhibitions of seed germination and growth were gradually strengthened with the increases of osmotic stresses,slight osmotic stress can promote seed germination. Under the same osmotic potential,the effects of PEG on TGPs and MGTs were stronger than that of NaCl. As the temperature increase,the seeds may change from photo-neutrality to photo-phobia. Decreased TGP under drought and continuous light interactive treatment is an adaptation strategy to avoiding drought. Hypocotyl growth accelerated under continuous dark treatment is an ecological trait which could increase dry matter input in stem and height for more light. Seed development under high concentration of NaCl treatment is better than that of PEG treatment due to low water potential caused by Na~+,which can enter into seed coat and promote water absorption.