Effects of salinity, alkalinity, temperature, and their interactions on seed germination and seedling growth of Salvia miltiorrhiza

Salviae miltiorrhizae is a traditional Chinese medicinal plant. The effects of four concentrations (6.25, 12.5, 25, and 50 mmol·L⁻¹) of salt solution and four concentrations (3.125, 6.25, 12.5, and 25 mmol·L⁻¹) of alkali solution on seed germination and seedling growth of S. miltiorrhiza seeds were studied under two varying temperatures (18 ℃/28 ℃ and 28 ℃/38 ℃). Salinity, alkalinity, temperature, and their interactions had significant effects on the seed germination and seedling growth of S. miltiorrhiza (P < 0.05). Seed germination and seedling growth were significantly higher under 18 ℃/28 ℃ than 28 ℃/38 ℃ (P < 0.05). Under 18 ℃/28 ℃ and 6.25 mmol·L⁻¹ salt solution, germination of S. miltiorrhiza was stimulated, with a significantly higher germination percentage and germination index than under water control (P < 0.05). Additionally, the relative salt damage rate was significantly lower than under water control (P < 0.05). There was no significant effect of 12.5 mmol·L⁻¹ salt solution and 3.125 mmol·L⁻¹ alkali solution on S. miltiorrhiza seed germination rate, germination index, and relative salt damage rate (P > 0.05). The germination rate and germination index of S. miltiorrhiza were decreased significantly under salt solution at 25 and 50 mmol·L⁻¹and alkali solution at 6.25, 12.5 and 25 mmol·L⁻¹ (P < 0.05), and the salt damage rate increased. Under 28 ℃/38 ℃, salt solution at 6.25 and 12.5 mmol·L⁻¹ and alkali solution at 3.125 and 6.25 mmol·L⁻¹ had no significant influence on the germination rate, germination potential, and relative salt damage rate of S. miltiorrhiza (P > 0.05). Salt solution at 25 and 50 mmol·L⁻¹ as well as alkali solution at 12.5 and 25 mmol·L⁻¹ significantly reduced the germination rate and germination index of S. miltiorrhiza (P < 0.05) and increased the relative salt damage rate. Salt and alkali stress inhibited root growth of S. miltiorrhiza seedlings significantly (P < 0.05). Under the two different temperature conditions, salt solution at 6.25 and 12.5 mmol·L⁻¹ and alkali solution at 3.125 mmol·L⁻¹ had no significant effect on leaf length growth of S. miltiorrhiza seedlings (P > 0.05), whereas 25 and 50 mmol·L⁻¹ salt solution and 6.25, 12.5 and 25 mmol·L⁻¹ alkali solution stress significantly inhibited leaf length growth (P < 0.05). Salt solution at 6.25 mmol·L⁻¹ under 18 ℃/28 ℃ promoted leaf width growth of seedlings, whereas salt solution at 6.25 mmol·L⁻¹ and alkali solution at 3.125 mmol·L⁻¹ under 28 ℃/38 ℃ had no significant effect on leaf width growth (P > 0.05). High salt and alkali stress significantly inhibited leaf width growth (P < 0.05). In conclusion, salinity, alkalinity, temperature, and their interactions had a significant effect on seed germination and seedling growth of S. miltiorrhiza. Salinity and alkalinity had relatively little impact on S. miltiorrhiza seeds under low temperature. Seed germination and seedling growth of S. miltiorrhiza were more sensitive to alkali stress. It is suggested that saline-alkali breeding of S. miltiorrhiza seeds should be carried out on land with low salinity and alkalinity and at a temperature of 18 ℃/28 ℃.