Prospecting for rare earth element (hyper)accumulators in the Paris Herbarium using X-ray fluorescence spectroscopy reveals new distributional and taxon discoveries

Abstract

Background

Rare earth elements (REEs) are increasingly crucial for modern technologies. Plants could be used as a biogeochemical pathfinder and a tool to extract REEs from deposits. However, a paucity of information on suitable plants for these tasks exists.

Methods

We aimed to discover new REE-(hyper)accumulating plant species by performing an X-ray fluorescence (XRF) survey at the Herbarium of the Muséum national d’Histoire naturelle (MNHN, Paris, France). We selected specific families based on the likelihood of containing REE-hyperaccumulating species, using known taxa that accumulate REEs. A total of 4425 specimens, taken in the two main evolutionary lineages of extant vascular plants, were analysed, including the two fern families Blechnaceae ( n = 561) and Gleicheniaceae ( n = 1310), and the two flowering plant families Phytolaccaceae ( n = 1137) and Juglandaceae ( n = 1417).

Key Results

Yttrium (Y) was used as a proxy for REEs for methodological reasons, and a total of 268 specimens belonging to the genera Blechnopsis ( n = 149), Dicranopteris ( n = 75), Gleichenella ( n = 32), Phytolacca ( n = 6), Carya ( n = 4), Juglans ( n = 1) and Sticherus ( n = 1) were identified with Y concentrations ranging from the limit of detection (LOD) >49 µg g ⁻¹ up to 1424 µg g ⁻¹. Subsequently, analysis of fragments of selected specimens by inductively coupled plasma atomic emission spectroscopy (ICP-AES) revealed that this translated to up to 6423 µg total REEs g ⁻¹ in Dicranopteris linearis and up to 4278 µg total REEs g ⁻¹ in Blechnopsis orientalis which are among the highest values ever recorded for REE hyperaccumulation in plants. It also proved the validity of Y as an indicator for REEs in XRF analysis of herbarium specimens. The presence of manganese (Mn) and zinc (Zn) was also studied by XRF in the selected specimens. Mn was detected in 1440 specimens ranging from the detection limit at 116 µg g ⁻¹ up to 3807 µg g ⁻¹ whilst Zn was detected in 345 specimens ranging from the detection limit at 77 µg g ⁻¹ up to 938 µg g ⁻¹.

Conclusions and Implications

This study led to the discovery of REE accumulation in a range of plant species, substantially higher concentrations in species known to be REE hyperaccumulators, and records of REE hyperaccumulators outside of the well-studied populations in China.