Using rhizosphere biogeochemistry to increase understanding of heavy metal bioavailability

A greater understanding of rhizosphere biogeochemistry is likely to improve our understanding of the factors that drive bioavailability of heavy metals in growth substrates. A glasshouse study was conducted that investigated the impacts of three growth substrates (topsoil, oxidised mining waste and unoxidised mining waste) and four species of New Zealand trees on the rhizosphere concentrations of arsenic, copper and zinc. In many of the substrate by species treatments the concentration of heavy metals was lower in the rhizosphere than in the bulk substrate. In addition, for a given plant species, where rhizosphere concentrations were significantly different to the bulk concentration, the rhizosphere concentration correlated better with plant shoot concentrations (i.e. bioavailability) than they bulk concentrations of heavy metals. In particular, the rhizosphere concentrations were good predictors of plant copper concentrations.