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.
Moradi AB , Swoboda S, Robinson B, Prohaska T, Kaestner A, Oswald SE, Wenzel WW , Schulin R (2010) Mapping of nickel in root cross-sections of the hyperaccumulator plant Berkheya coddii using laser ablation ICP-MS. Environmental and Experimental Botany 69(1), 24-31.
Moradi AB, Oswald SE, Nordmeyer-Massner JA, Pruessmann KP, Robinson BH, Schulin R (2010). Analysis of nickel concentration profiles around the roots of the hyperaccumulator plant Berkheya coddii using MRI and numerical simulations. Plant and Soil 328(1-2), 291 - 302.
Moradi AB, Conesa HM, Robinson BH, Lehmann E, Kaestner A, Schulin R (2009). Root responses to soil Ni heterogeneity in a hyperaccumulator and a non-accumulator species. Environmental Pollution 157, 2189–2196.
Robinson BH, Kim N, Marchetti M, Moni C, Schroeter L, van den Dijssel C, Milne G, Clothier BE (2006). Arsenic hyperaccumulation by aquatic macrophytes in the Taupo Volcanic Zone, New Zealand. Environmental and Experimental Botany 58(1-3), 206-215.
Keeling SM, Stewart RB, Anderson CWN, Robinson BH (2003). Nickel and cobalt phytoextraction by the hyperaccumulator Berkheya coddii: implications for polymetallic phytomining and phytoremediation. International Journal of Phytoremediation 5(3), 235-244.
Robinson BH, Brooks RR, Hedley MJ (1999). Cobalt and nickel accumulation in Nyssa (tupelo) species and its significance for New Zealand agriculture. New Zealand Journal of Agricultural Research 42, 235-240.
Robinson BH, Brooks RR, Howes AW, Kirkman JH, Gregg PEH (1997). The potential of the high-biomass nickel hyperaccumulator Berkheya coddii for phytoremediation and phytomining. Journal of Geochemical Exploration 60, 115-126.
Robinson BH, Chiarucci A, Brooks RR, Petit D, Kirkman JH, Gregg PEH, de Dominicis V (1997). The nickel hyperaccumulator plant Alyssum bertolonii as a potential agent for phytoremediation and the phytomining of nickel. Journal of Geochemical Exploration 59, 75-86.