The Study On The Effects Of Different Stress On Germination And Early Seedlings Of Medicago Ruthenica

Medicago ruthenica, a perennial legume, can be found in northern China on open hillsides, mixed grass steppes, and meadows. It is also distributed in Songnen grassland in northeast of China. Seed germination is the initiative and crucial stage in the life cycle of plants, which influences the seedling establishment and subsequent development. So in this article we discussed the effects of different stress such as salinity, alkalinity, drought and temperature on germination of Medicago ruthenica.In the first chapter, (1)we studied the responses of germination stage and early seedlings of two ecotypic M. ruthenica (Linxia and Caodian) grew in Songnen grassland, which were forced by NaCl (0, 50, 100, 150, 200, 250mM) and with three ranges of alternating temperatures (10-20, 15-25, 20-30℃), (2)we compared with PEG (0, 50, 100, 150, 200, 250g/L), Na₂CO₃ (1, 5, 10, 15, 20, 25mM) and with three ranges of alternating temperatures (10-20, 15-25, 20-30oC) to determine the effects of the interactions between salinity and temperature, drought and temperature, and between alkalinity and temperature. The results indicated that (1)the growth of radical was inhibited by NaCl, but low concentrations of NaCl can promote the growth of hypocotyl. (2)the two ecotypic M. ruthenica could germinate in higher salt concentrations. The highest concentration could reach to 250 mM NaCl, 200 g/L PEG and 25 mM Na₂CO₃. From the germination aspect, Linxia grew better than Caodian which were treated with NaCl and Na₂CO₃, but the situations were reversed when they were stimulated by some concentrations of PEG.In the second chapter, we studied the germination responses of M. ruthenica(L.) Ledebour seeds to constant temperature (5, 10, 15, 20, 25, 30, 35, 40°C), salinity (0, 50, 100, 150, 200, 250 mM), alkalinity (1, 5, 10, 15, 20, 25 mM), and three ranges of alternating temperature (10-20, 15-25, 20-30°C) were used to determine the salinity and alkalinity effect, as well as the effect of interactions between salinity and temperature and between alkalinity and temperature, and the germination responses of M. ruthenica(L.) on different salts such as NaCl, KCl, Na₂SO₄, K₂SO₄, NaHCO₃, KHCO3. The results indicated that the seeds of M. ruthenica(L.) germinated in a high percentage at a wide range of temperature regimes except at 5°C and germinated well in lower NaCl and Na2CO3 concentrations at all the three alternating temperatures. Approximately half of the seeds can also germinate in high salinities and alkalinities at optimum temperature (15-25°C). Furthermore, the un-germinated seeds keep alive during the exposure to the high saline and alkaline stress for a short period. These results suggested that M. ruthenica(L.) adapted saline and alkaline environments and it is a promising legume forage to be developed in this area, and can be used to establish artificial grassland to recover Songnen grassland.