Spatially Resolved Localization of Lanthanum and Cerium in the Rare Earth Element Hyperaccumulator Fern Dicranopteris linearis from China

The fern Dicranopteris linearis (Gleicheniaceae) from China is a hyperaccumulator of rare earth element (REE), but little is known about the ecophysiology of REE in this species. This study aimed to clarify tissue-level and organ-level distribution of REEs via synchrotron-based X-ray fluorescence microscopy (XFM). The results show that REEs (La + Ce) are mainly colocalized with Mn in the pinnae and pinnules, with the highest concentrations in necrotic lesions and lower concentrations in veins. In the cross sections of the pinnules, midveins, rachis, and stolons, La + Ce and Mn are enriched in the epidermis, vascular bundles, and pericycle (midvein). In these tissues, Mn is localized mainly in the cortex and mesophyll. We hypothesize that the movement of REEs in the transpiration flow in the veins is initially restricted in the veins by the pericycle between vascular bundle and cortex, while excess REEs are transported by evaporation and cocompartmentalized with Mn in the necrotic lesions and epidermis in an immobile form, possibly a Si-coprecipitate. The results presented here provide insights on how D. linearis regulates high concentrations of REEs in vivo, and this knowledge is useful for developing phytotechnological applications (such as REE agromining) using this fern in REE-contaminated sites in China.