Fluoride hyperaccumulation in

Abstract

Members of the Australian endemic plant genus Gastrolobium (Fabaceae) naturally accumulate fluoride (F) in the form of fluoroacetate when growing on soils with very low F status. However, it is unknown how Gastrolobium species respond to higher soil F concentrations, and what the interactions are between cations (Na+, Mg2+, K+, Ca2+) and anions (Cl−, F−, SO42−) in their leaves. In this study, we exposed G. bilobum, G. parviflorum and G. parvifolium to soils with different levels of soluble F− (as sodium fluoride solution applied to soil at 0, 1, 10, 50, 100 μg F g−1). The plants were grown for a period of 12 months before being harvested and acid- and water-extractable F in shoots analysed using ion chromatography. Gastrolobium leaves accumulated extremely high F with highest concentrations in young leaves in the highest treatment level. In G. parviflorum, the mean concentration of F in young leaves was >8000 μg g−1 for both methods of extraction, whereas G. parvifolium had 6940 and 3630 μg g−1 in young leaves for the water-soluble and acid extraction methods respectively. In young leaves of G. bilobum, the concentration of F was 1840 and 7970 μg g−1 for the water-soluble and acid extraction methods respectively. This study further revealed significant amounts of Cl− and SO42− in foliage of the studied species. Moreover, we found F− and SO42− to be positively correlated in young leaves of G. bilobum, but inversely related in its old leaves. These findings have shown for the first time the potential of Gastrolobium species to accumulate F in soils with high F concentrations, highlighting potential for applications in phytoremediation.