Effect of organic acids application on zinc uptake and accumulation by two ecotypes of Sedum alfredii Hance

A solution culture experiment was carried out to compare the influences of organic acids application on zinc (Zn) uptake and accumulation by two ecotypes of Sedum alfredii Hance. The results indicated that addition of citric acid or oxalic acid enhanced the tolerance of nonaccumulating ecotype of Sedum alfredii to Zn toxicity,but had no obvious effects on the growth of the hyperaccumulating ecotype. Addition of citric acid, oxalic acid or both increased Zn concentration in leaf, stem especially root for the nonaccumulating ecotype. Zinc concentrations in the roots treated with these organic acids were 4～5 times higher than treated with only Zn. However, application of citric acid, oxalic acid or both had no obvious effects on Zn concentration in leaf and stem of the hyperaccumulating ecotype, except that root Zn concentration was increased by organic acid treatments. The Zn accumulation in both roots and shoots of the nonaccumulating ecotype was enhanced by organic acids addition, by citric acid addition in particular. Whereas slight increase in root Zn accumulation but no influence on shoot Zn accumulation were noted for the hyperaccumulating ecotype when grown at external addition of citric acid, oxalic acid or both. The concentration of water soluble Zn increased in leaves and stems, but its proportion to the total Zn concentration decreased by addition of organic acids for the nonaccumulating ecotype. For the hyperaccumulating ecotype, however, similar changes in water soluble Zn and its proportion to total Zn in stems were noted among the treatments. Application of organic acids increased water soluble Zn and its proportion to the total in the leaves of the hyperaccumulating ecotype. The results implied that citric acid or oxalic acid might be as ligand with Zn to reinforce Zn absorption, transportation and immobilization in roots, and Zn in leaves and stems may exist as the complex with soluble organic compounds or as soluble inorganic salts.