Effects of cadmium and nickel single and combined stress on the seed germination and seedling growth of three herbaceous plants

The aim of this study was to assess and compare the tolerance levels of three herbaceous plants, Pennisetum americanum × P. purpureum, Melilotus officinalis, and Festuca arundinacea, towards cadmium and nickel stress. The objective was to expand the range of species suitable for rehabilitating soils contaminated with these metals. Seed germination tests and seedling growth experiments were conducted using seeds obtained from these plants. The results indicated that the germination rate of the three plants was highest at a specific cadmium concentration of 10 mg·L⁻¹ compared to the control group. Similarly, the vigor index reached its maximum value at a specific nickel concentration of 10 mg·L⁻¹. When exposed to combined cadmium-nickel stress at a concentration of 10 mg·L⁻¹, Pennisetum americanum × P. purpureum exhibited a significantly greater vigor index, F. arundinacea showed a increase in germination index, and M. officinalis demonstrated a increase in total dry weight compared to the control group. The germination and seedling growth of the three plants were hindered by increased levels of cadmium and nickel, both individually and in combination. The combined stressors of 200 mg·L⁻¹ cadmium and 300 mg·L⁻¹ nickel had the most significant inhibitory effects on plant growth, as indicated by decreased vigor index and root length. The study also evaluated the cadmium tolerance traits of the three plants and found that they all exhibited a certain level of tolerance to cadmium stress, with P. americanum × P. purpureum showing the highest tolerance. This suggests that P. americanum × P. purpureum have potential as remediation species in cadmium-contaminated soils.