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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.

Cited Reference Count: 42 ref.Csirohttp://www.publish.csiro.au/nid/102.htmfrancois.beaujard@clermont.inra.fr; International audience; Tree nutrient research concentrated on endogenous C and N remobilisation in spring has neglected to acknowledge the possibilities of significant effects of N uptake before bud break, especially on the quality of regrowth and N reserve remobilisation. To investigate this subject, experimental studies were performed on young poplars (Populus tremula x Populus alba, clone INRA 717-1B4) grown with a controlled nutrient supply: (i) without N, 'control'; (ii) N supplied throughout the course of the experiment, 'N-supply'; and (iii) N supplied only before bud break, 'N-pulse'. Results confirm the hypothesis that poplar scions can significantly take up nitrate before bud break, amounting to similar to 34% of the total N stored the previous year. After bud break, emerging leaves restart the sap flow, which increased nitrate uptake to support the regrowth. N-pulse and N-supply treatments were found to have significant effects shortly after a growth period, i. e. by increasing N content of all tissues (e.g. 37 and 81% in new shoots respectively), leaf area (18 and 29%) and specific leaf area (20 and 35%). Therefore, results confirm the hypothesis that early N supply plays a significant role in the N status and N remobilisation involved in the spring regrowth of young trees.