Plant-soil relations of selenium, molybdenum and vanadium in the Richmond District of Central Queensland, Australia

Background and aims: The Richmond District of Queensland (Australia) hosts seleniferous soils and is the habitat of selenium (Se) hyperaccumulator plants. These soils are also naturally enriched in vanadium (V) and molybdenum (Mo). This study aimed to survey soils and plants of the Richmond area with a focus on the Se hyperaccumulator Neptunia amplexicaulis. Methods: Field collection of plant specimens and soils from the seleniferous outcrops of the Richmond District (including the Julia Creek area) was undertaken and the samples were analyzed for Se, V, Mo and other elements. Results: The results show that three modes of Se accumulation can be observed with most plant species having from ~10 μg Se g⁻¹ up to 70 μg Se g⁻¹ in shoots, some having between 75 and 250 μg Se g⁻¹in shoots while both N. amplexicaulis and Acacia tephrina contained 450–700 μg Se g⁻¹ in their shoots. There was high Se accumulation in the phyllode tips of A. tephrina. Previously unrecorded populations of N. amplexicaulis were discovered near Julia Creek. Selenium concentrations in soil are lower than historically reported from similar localities (up to 23.2 mg Se kg⁻¹). Molybdenum concentrations between 213 and 329 μg Mo g⁻¹ occurred in the two Se hyperaccumulators N. amplexicaulis and A. tephrina, whilst Salsola australis had the highest accumulation of V (31–66 μg V g⁻¹). Conclusions: The results suggest that the Toolebuc Formation is the source of Se in the region, but temporal variability alters how much Se is bioavailable to plants. The presence of high Mo in plant tissues is linked to Se hyperaccumulation, and V accumulation appears to have little impact on plant ecology.