Germination responses of Alfalfa ( Medicago sativa L.) seeds to various salt-alkaline mixed stress

Salinization and alkalization in soil frequently co-occur in agriculture ecosystem, and directly affect plant production. Alfalfa (Medicago sativa) is important forage with good quality and high yield. Its production is markedly influenced by those attributes of soils, especially mixed salt-alkali stress. However, the knowledge on seeds germination linked to mixed salt-alkali stress received little attention, though seeds germination influence plant yields. In this study, we assessed that the effects of 30 mixed salt-alkali combinations (NaCl, Na2SO4, NaHCO3, and Na2CO3; salinity 24 to 120 mmol/L and pH 7.03 to 10.69) on germination of alfalfa seeds. Our results showed that the interaction of salinity and alkalinity significantly affected germination rates of alfalfa seeds. The interactive effects between salinity and alkalinity resulted in changes in radicle length and plumule length of alfalfa seeds. The study also indicated some physiological responses (electrolyte leakage rate, proline content, soluble sugar, and Na+/ K+) of alfalfa seeds were affected by mixed salt-alkaline stress. The experimental results concluded that mixed salt-alkaline stress emphasizes the interaction between salt concentration and salt component, and differs from salt or alkali stress, and elucidated that seeds germination of plants may adapt to mixed salt-alkaline environment through modifying physiological mechanisms in plants.   Key words: Medicago sativa L., seed, germination, salinity, alkalinity, mixed salt-alkaline, stress.