Metal Hyperaccumulator Plants: A Review of the Ecology and Physiology of a Biological Resource for Phytoremediation of Metal-Polluted Soils

The concentrations in plant parts depend both on intrinsic and extrinsic factors and vary greatly for different species and for different metals. Responses by plant species to exposure to metalliferous soils can range from phytotoxicity to survival by exclusion, with only small elevations of metal concentration to survival with accumulated metal constituting a significant percentage of the plant dry matter. The importance of nonvascular transport through laticifers, for example, is also obscure. The extent to which secondary xylem tissues become a long-term repository for accumulated metals is not known. The high degree of endemism to metal-rich soils shown by hyperaccumulating taxa has been related to their survival. The success of many metallophytes in overcoming the adverse edaphic conditions is such that they can exist relatively free from competition. Metal hyperaccumulators have been recognized on the basis of concentrations of metals in leaf dry matter.