Rare earth elements (REEs), aluminum and silicon interactions in the fern Dicranopteris linearis from China

Wen-Shen Liua, A. van der Entb, J.S. Lairdc, Y.T. Tanga and R.L. Qiua

a School of Environmental Science and Engineering, Sun Yat-sen University, China

b Sustainable Minerals Institute, The University of Queensland, Australia

c School of Physics, University of Melbourne, Australia

liuwsh3@mail2.sysu.edu.cn

Dicranopteris linearis is a fern that accumulates unusually high concentrations (up to 0.3% dry weight) of rare earth elements (REEs) in China. Previously, we reported that D. linearis accumulates high concentration of aluminium (Al) and silicon (Si) in the fronds, but the interactions between these elements and REEs are unknown. In this study, a range of analytical techniques, including extractions, Scanning-Electron Microscopy with Energy-Dispersive Spectroscopy (SEM-EDS) and Particle Induced X-Ray Emission (PIXE) were used to study the associations of REEs with Al and Si. The results showed that D. linearis accumulated high concentrations of REEs (up to 3830 mg kg-1), Al (up to 9660 mg kg-1) and Si (up to 20 300 mg kg-1), with concentrations increasing with the age and the frond order of the pinna. The PIXE analysis revealed that REEs (e.g. La & Ce) were highly concentrated within the veins and necrosis of the pinnules, which were probably induced by manganese toxicity. While Al and Si were more concentrated at the margins of the pinnules. The PIXE analysis also revealed that REEs, Al and Si were co-localized at the xylem and pericycle (cell walls) of the stolon, petiole and midvein cross-sections, the epidermis especially the upper epidermis of the pinnule cross-section. The extraction patterns suggested the existence of REEs-Si and Al-Si complexes in the fronds. The SEM-EDS analysis confirmed the existence of aluminosilicate deposits in the protoplast and apoplast of the pinna cells, and cell walls of the pericycles of the vascular system. We speculate that REEs, Al and Si were co-existing within the solutes of the transpiration flow, and then, some of which were carried to the blades and co-deposited at the epidermis and necrosis, and some that did not translocate out were co-deposited at the pericycle. Overall, our results show that REEs/Al-Si co-depositions are involved in detoxifying the excess REEs and Al in D. linearis frond.

This work was supported by the National Natural Science Foundation of China (NSFC) [Grant No. 41771343], and the 111 project [Grant No. B18060]. The “International Joint Lab - ECOLAND” is acknowledged for supporting this work. A. van der Ent is the recipient of a Discovery Early Career Researcher Award [Grant No. DE160100429] from the Australian Research Council.

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