Phytotoxicity and accumulation of lead in Australian native vegetation

Lead (Pb) is a wide spread contaminant in the terrestrial landscape. It is highly detrimental to plant and animal life and possesses no known biologic function. Yet there is a paucity of reliable information available on the response of Australian and other plant species to Pb exposure at phytotoxic doses. In this study, the response of three Australian native grass species and two tree species to Pb in nutrient solution culture was investigated. Plants were exposed to average Pb concentrations ranging from 0.020 to 15.2 microM. The plant species included Acacia decurrens, Austrodanthonia richardsonii, Bothriochloa macra, Eucalyptus camaldulensis, and Dichanthium sericeum. Few foliar symptoms were evident in any plant species, although some discolouration in young leaves of E. camaldulensis was evident from 1 microM, and B. macra showed pronounced reddening at the highest treatments. The most tolerant plant species studied based on solution EC(50, roots) (microM) results was B. macra (7.0 +/- 0.2), followed by A. decurrens (3.9 +/- 0.2), D. sericeum (2.9 +/- 0.3), E. camaldulensis (1.1 +/- 0.3), and A. richardsonii (0.4). A hazardous concentration value (HC(5)) (n = 9) for soil solution was estimated to be 0.16 microM. A. richardsonii was highly sensitive to Pb and possessed little ability to restrict Pb translocation to its shoots. B. macra was able to tolerate high root (3924 mg kg(-1)) and shoot (743.0 mg kg(-1)) Pb concentrations. A. decurrens excluded Pb from it shoots. The high tolerance of A. decurrens to Pb and limited translocation to shoots indicates it may be useful in revegetation of Pb-contaminated soils.