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Recent studies have shown that various fern species can accumulate REEs in the soil and may be utilized as indicator plants. Athyrium yokoscense, commonly called hebino negoza in Japan, is a pteridophyte that is used as an indicator of metal-contaminated soils in Japan. Mining and mineral processing increase the potential of mine minerals to oxidize and change their chemical form. A study on the biogeochemical behavior of REEs in the mine area needs to be conducted due to the significant use of REEs as an essential material for various applications in the world. The REE content in sediment and pteridophytes under different mining areas was analyzed by inductively coupled plasma-mass spectrometry. The concentration of REEs contained in Athyrium yokoscense was analyzed and then compared to sediment to determine the ability of the plant to absorb and accumulate rare earth elements in the mine area. Sediment and plant samples were collected from three mining areas: Ikuno mine, Akenobe mine, and Tada mine. Athyrium yokoscense plants were collected and digested with hydrogen peroxide (H₂O₂) and nitric acid (HNO₃) at a ratio of 2:5. Sediment samples were taken and digested by the alkali fusion method using lithium tetraborate and then processed using the conventional column method. The present study determined that the concentration of REEs varies in every location, and light REEs tend to be more abundant in sediments than heavy REEs. The amount that can be transferred to ferns also varies. Athyrium yokoscense in the ex-mining area accumulates proportionately more LREEs than HREEs, specifically in the Athyrium yokoscense leaves. The characteristic of the element significantly contributes to the accumulation of REEs in pteridophytes. Full article

The fern Athyrium yokoscense often flourishes around mine sites in Japan and can tolerate and accumulate heavy metals such as lead (Pb) and cadmium (Cd). In this work, we examined whether proanthocyanidins, also called condensed tannins, were involved in the mechanisms of Pb and Cd tolerance and accumulation of A. yokoscense because proanthocyanidins are known to alleviate metal stress in several plant species and are present at high levels in A. yokoscense. For this purpose, we used mutant gametophytes deficient in proanthocyanidins, in which the relative proanthocyanidin contents were 20% of those of the wild-type gametophytes. Although the proanthocyanidin contents of the mutant were quite low, the growth of the mutant was very similar to that of the wild-type gametophytes even in the presence of 80 mg/kg Pb or 48 mg/kg Cd. Under the same conditions, the mutant gametophytes also accumulated Pb and Cd as much as the wild-type gametophytes did. These results indicate that the proanthocyanidins in A. yokoscense are not important for the Pb and Cd tolerance and accumulation properties. Full article