The variation of REE (rare earth elements) patterns in soil-grown plants: a new proxy for the source of rare earth elements and silicon in plants

Rare earth elements (REEs) in five species of soil-grown plants (Taxodium j aponicum, Populus sieboldii, Sasa nipponica, Thea sinensis and Vicia villos a) and in the soil on which each plant grew were determined with an inducti vely coupled plasma mass spectrometer (ICP-MS) in order to observe the vari ation in the distribution of REEs and to elucidate their source in soil-gro wn plants. The plant samples were divided into root (secondary root and mai n root), trunk (stem) and leaf; the soils into water soluble (soil(soluble fraction)), HCl and HNO3 soluble (soil(non-silicate fraction)) and HF solub le (soil(silicate fraction)). The REE abundances of samples were compared u sing REE patterns where the abundances were normalized to those of a chondr ite and plotted on a logarithmic scale against the atomic number. All the p lants showed similar REE patterns independent of species and location, and a W-shape variation (W-type tetrad effect) and abundance depletion of ceriu m (negative Ce anomaly) were found in each REE patterns of plants, more con spicuous tetrad effect being observed in HREE (heavier rare earth elements) region than in LREE (lighter rare earth elements) region. The overall vari ation of REE patterns of each secondary root was not similar to that of soi l(soluble fraction), but similar to that of soil(silicate fraction) except for the tetrad effect and Ce anomaly. The REE patterns can be interpreted b y the idea that plants of different species take in REEs and Si from differ ent parts in the soil. The results of this study seem to imply that Sasa ni pponica and Vicia villosa take in free REEs and Si rather directly from sil icate in the soil, and that a majority of REEs and Si in Taxodium japonicum and Thea sinensis are originated from the soluble fraction in the soil.