Abstract: Effects of Ca²⁺ with different concentrations on some earlier physiologic and ecological characteristics of seed germination of Casuarina equisetifolia under chromic stress were studied. The results showed that the seed germination and the seedling growth were inhibited under the Cr³⁺ stress with concentrations of 10mg·L^-1 or 100mg·L^-1, and there was stronger toxic effect with higher Cr³⁺ concentration. When seeds or seedlings were treated by Ca²⁺ with proper concentration, although the plants were still under the Cr³⁺ stress, the content of proline,O₂^- and MDA, and the activities of POD and CAT were decreased, and SOD activity increased.Therefore, Ca²⁺ reduced the inhibition of seed germination and seedling growth. There was a good modulation effect of Ca²⁺ on accelerating the seed germination and enhancing the activity of seedling protective enzymes under Cr³⁺ stress. Ca²⁺ could also modulate the sensitivity of proline to stress response, decrease the speed of O₂^- production, and alleviative the peroxidation degree of membrane lipid. But the treatment of Ca²⁺ needed suitable concentration.Much too high Ca²⁺ concentration would bring negative effect. The proper concentration of Ca²⁺ was in the range of 0.01～1mmol·L^-1 .

Key words: Microcystis aeruginosa, Phosphate, Aqueous ecosystem, Temperature, Translocation, Isotope tracer