Abstract: A vermiculite pot culture experiment was conducted to study the effects of low, medium, and high concentrations of CaCl₂ on the Cd accumulation and stress of Spartina alterniflora. At 200 μg·g^-1 of CdCl₂, the S. alterniflora plant height, tiller number, catalase activity, and shoot and root dry weights decreased somewhat, while the plant proline content increased significantly. With the supplement of increasing concentration of CaCl₂, the plant height, tiller number, catalase activity, and shoot and root dry weights decreased after an initial increase, indicating that definite concentration of CaCl₂ increased the Cd tolerance of S. alterniflora. As compared with CdCl₂ stress alone, the supplement of CaCl₂ decreased the plant proline content, suggesting the mitigation effect of CaCl₂ on the toxic effect of Cd on S. alterniflora. The Cd was mainly accumulated in the underground part of S. alterniflora.  With the increasing concentration of supplemented CaCl₂, the Cd concentration in the above and underground parts of S. alterniflora and the Cd transfer coefficient increased significantly, suggesting that CaCl₂ had definite activation effect on Cd, and helped to increase the capability of S. alterniflora in absorbing Cd and transporting the Cd to the plant aboveground part.

Key words: landscape connectivity, distance threshold, ecological security, the middle reaches of the Heihe River., ecological land