Plant cultivation and salt treatments
Seeds of S. alterniflora were sampled and the fully developed seeds were picked out and vernalized at 4 oC for at least 4 weeks. After vernalization, every five seedlings with same size were planted in a pot (14 cm height, 12 cm diameter) with clean sands. The young seedlings were irrigated with 1/2 strength Hoagland solution and grown in greenhouse for 2 weeks. The environmental condition in greenhouse was set as followed: 50-70% relative humidity, 25-28oC daily temperature, 12/12 h day/night photoperiod and 700-1000 μmol m-2 s-1 light intensity.
After 2 weeks, the seedlings with same size were divided into three groups. Seedlings in group 1 were irrigated with full-strength Hoagland solution without sea salt (0‰ salinity); seedlings in group 2 were irrigated with full-strength Hoagland solution with 15‰ sea salt (15‰ salinity); seedlings in group 3 were irrigated with full-strength Hoagland solution with 30‰ sea salt (30‰ salinity). At the beginning of salt treatment, the salinity in group 2 and group 3 were gradually increased by 5‰ every days until reached the preset salinity condition. The Hoagland solution with or without salt addition were replaced every 3 days to maintain the preset salinity. Each salinity treatments had at least 150 seedlings. The seedlings subjected to different salinity treatments were grown in greenhouse for 150 days. Each treatment had 3 replicates.