Global Distribution and Ecology of Hyperaccumulator Plants

A large body of analytical data is available on the inorganic composition of many thousands of plant species, for which typical concentration ranges have been tabulated for major, minor, and trace elements. These elements include those that have been shown essential for plant growth, as well as others that lack this status, at least universally. Metalliferous soils, having abnormally high concentrations of some of the elements that are generally present only at minor (e.g. 200–2000 μg g−1) or trace (e.g. 0.1–200 μg g−1) levels, vary widely in their effects on plants and have attracted increasing attention during the last 50 years. The effects depend on the species, the relevant elements, and soil characteristics that influence the availability of metals to plants. Some of these soils are toxic to all or most higher plants. Others have hosted the development of specialized plant communities consisting of a restricted and locally characteristic range of metal-tolerant species. These plants often show a slightly elevated concentration of the elements with which the soil is enriched, but in places a species exhibits extreme accumulation of one or more of these elements, to a concentration level that may be hundreds or even thousands of times greater than that usually found in plants on the most common soils. These plants, now widely referred to as hyperaccumulators, are a remarkable resource for many types of fundamental scientific investigation (plant systematics, ecophysiology, biochemistry, genetics, and molecular biology) and for applications such as phytoremediation and agromining, and are discussed in detail below.