Response of seed germination, seedling growth and physiological characteristics to alkali stress in halophyte Suaeda liaotungensis.

Soil salinization has been considered as a major environmental threat to plant growth. Different types of salt in saline soil have different effects on germination and seedling growth. Effect of NaCl on germination and seedling establishment in Suaeda liaotungensis have been reported, but its response to alkali stress remains unclear. Our results showed that brown seeds had higher germination rate, however, black seeds had higher germination recovery percentage under alkali stress. Na₂CO₃ had stronger inhibitory effect on germination and seedling growth than NaHCO₃. As the concentration of alkali stress increased, the ROS level of brown seeds gradually ascended, while that of black seeds decreased first and then ascended. MDA content of dimorphic seeds significantly increased under alkali stress. The trend of SOD, POD and CAT activity between dimorphic seeds was similar under the same type of alkali stress. Alkali stress enhanced proline content of dimorphic seeds, and dimorphic seeds in NaHCO₃ solution had higher proline content than Na₂CO₃ solution. Moreover, radicle and shoot tolerance indexes of seedlings in NaHCO₃ solution were significantly higher than that of Na₂CO₃ solution. Under strong alkali stress, seedlings in NaHCO₃ solution had significantly lower ROS level and MDA content as well as higher antioxidant enzyme activity than Na₂CO₃ solution. This study comprehensively compared the morphological and physiological characteristics in germination and seedlings to better reveal the saline-alkali tolerance mechanisms in S. liaotungensis.