Seasonal changes in concentrations of trace elements and rare earth elements in shoot samples of Juncus effusus L. collected from natural habitats in the Holy Cross Mountains, south-central Poland.

Selected trace elements (Ag, As, Ba, Bi, Cd, Co, Cr, Mn, Cu, Fe, Ni, Pb, Tl, U, Zn) and rare earth elements were determined in 13 samples of Juncus effusus collected from three investigation sites in the Holy Cross Mts., south-central Poland. Sampling was carried out four times during a vegetative season of 2014. Almost all the elements examined showed different seasonal trends in their concentrations, except for Ag, Co and Ni. Maximum concentrations of Ag in samples of three investigation sites were found in May (0.068, 0.062, 0.047 mg/kg) whereas Co (0.124, 0.070, 0.079 mg/kg) and Ni (1.8, 0.998, 2.8 mg/kg) in July, respectively. Mean concentrations of Mn and Cd were higher in shoots (558 and 2.35 mg/kg) than in roots (435 and 1.7 mg/kg). Both these elements revealed much higher concentrations in J. effusus than their typical contents in plant samples. Principal component method allowed us to allocate Ni, Ba, Cd and Cu to one group with the highest positive loadings. The most probable explanation for this correlation is that bioavailability of these metals is increased by J. effusus through a release of oxygen to the rhizosphere. Light rare earth elements concentrations predominate over heavy rare earth elements in the samples examined. A fractionation of lanthanides occurs during their transport from roots to shoots, although this transport is rather limited. All shoot samples have a strong positive Eu anomaly.