Identification of new hardy ferns that preferentially accumulate light rare earth elements: a conserved trait within fern species

Abstract

Environmental contextRare earth elements (REEs) are strategic metals and emerging contaminants for which plant-based remediation measures are needed. We screened a collection of hardy ferns and identified new accumulator species that preferentially transferred light REEs to their fronds. This study is an important step towards understanding the mechanisms of REE accumulation in plants. AbstractRare earth elements (REEs) include the lanthanides plus yttrium and scandium, and can be split according to their atomic mass into light (LREEs) and heavy REEs (HREEs). The increasing demand for REEs is mainly driven by new technologies, and their current low recyclability has led them to become emerging contaminants. The identification of new REE accumulators may help in determining the REE transfer mechanisms and may result in interesting candidates for phytoremediation techniques. To that end, a collection of 49 hardy fern species, grown in REE-spiked substrate, were screened for their potential in REE accumulation. REE concentrations were very low in the fronds of all Polypodium species, whereas all Athyrium species highly accumulated REEs. The REE accumulation level was more variable among the different species of Dryopteris, Blechnum, Woodwardia, Cystopteris and Polystichum. However, whatever the species, LREEs were preferentially transferred to the fronds over HREEs. This conserved trait was independent of the availability of different REEs in the substrate and instead may arise from specific transfer systems in ferns for the two groups of REEs. Furthermore, REE accumulation was correlated to Ca and Al, which suggested the existence of common uptake pathways. Altogether, these results are of great interest for phytoremediation purposes since appropriate species can be chosen according to the area to be remediated, and they also provide new insights into a more in-depth characterisation of the underlying REE accumulation mechanisms in ferns.