Hyperaccumulator plants
Hyperaccumulator plants accumulate inordinate amounts of one or more Trace Elements (TE)s in their above ground biomass. Hyperaccmulators can have TE concentrations in their dry biomass that are 100 times higher than non-hyperaccumulators growing in the same soil. For most TEs a common threshold concentration for a plant to be considered a TE hyperaccumulator is 0.1%. For zinc and manganese, the threshold concentration is 1% and for cadmium, the threshold concentration is 0.01%. At present, there are over 400 species of known hyperaccumulators. A continual stream of new discoveries adds to this list. Hyperaccumulators species may accumulate one or more of a range of TEs that currently includes nickel, manganese, zinc, cadmium, thallium, copper, cobalt and arsenic.
The hyperaccumulation trait has evolved (or was, er, created) several times, as it is occurs in several families in the plant kingdom. Many hyperaccumulators belong in the Brassicaceae. One current mystery is what, if any, advantage does TE hyperaccumulation confer on the plant. Five theories are:
- tolerance to, or disposal of, the TE from the plant,
- a drought-resistance strategy,
- a means of avoiding competition from less TE-tolerant plants,
- inadvertent uptake of TEs,
- defence against herbivores or pathogens.
Despite the obvious appeal of the herbivore defence theory, studies have shown that, in many cases, TE accumulation does not protect the plant from herbivore attack.
Hyperaccumulator species mostly occur on ultramafic (serpentine) or calamine soils. Their presence is often an indication of elevated soil heavy-metal concentrations and hence they can function as bioindicators of mineralization and contamination. Hyperaccumulators have a potential role in the mining industry where they may find use for phytomanagement and phytomining.
Our current research focuses on the use of hyperaccumulators for the phytomanagement of TE-contaminated sites.
