Fluoride hyperaccumulation in Gastrolobium species (Fabaceae) from Western Australia

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.