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

Highlights

• Peak level of Ag in shoots of J. effusus occurred in May whereas Co and Ni in July.

• Mn and Cd are enriched in shoots exceeding by far their typical contents in plants.

• Ni, Ba, Cd and Cu show high positive correlations in shoots of J. effusus.

• Plant samples are enriched in light rare elements, shoots show a strong Eu anomaly.

• Transfer of rare earth elements from roots to shoots is very low.

Abstract

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.

Introduction

Juncus effusus is an emergent, perennial macrophyte growing in different parts of the world, including the temperate areas in Europe, Asia and North America, except for arid and mountainous areas. J. effusus prefers moist and wet soils, especially in sunny locations (Huxley, 1992). This plant species has gained a broad scientific interest for its many applications, including the use in medicine (Peng et al., 2018), production of natural fungicides for sustainable agriculture (Thuerig et al., 2016), as well as in: phytoremediation (Sun and Saeed, 2009), phytostabilization (Najeeb et al., 2017), phytovolatilization (Wiessner et al., 2013) and phytodegradation (Syranidou et al., 2017).

It has been shown that J. effusus can effectively remove both inorganic contaminants including arsenic, chromium, zinc, ammonium and organic pollutants as well as a mixture of inorganic and organic contaminants from wastewater and soil (Matthews et al., 2004, Bouldin et al., 2006, Gruber et al., 2008, Rahman et al., 2014, Lizotte and Moore, 2017, Syranidou et al., 2017, Zhang et al., 2017). Metals and metalloids are among the most often studied inorganic contaminants that can be removed from wastewater or soil using J. effusus. Because, similarly to many halophytes, J. effusus has a high resistivity to toxic metals, and therefore it is recommended for treatment of wastewater abundant in Zn, Mn, Cd, Cr, and Cu. Despite a high tolerance to toxic metals shown by J. effusus, some authors reported adverse physiological response to high concentrations of ions in the treated wastewater. Gruber et al. (2008) found that a maximum concentration of potassium dichromate in wastewater not affecting J. effusus was 34 μM. Addition of chelating agents, such as citric acid, to contaminated substrate improves Mn phytoextraction with the use of J. effusus, and alleviates the negative symptoms (Najeeb et al., 2009).

Efficiency of the removal of contaminants by J. effusus has usually been studied under controlled conditions (hydroponic experiments with synthetic wastewater and mesocosm studies), and some of the experiments were also performed under field conditions (Syranidou et al., 2017). The least frequently reported are studies of samples collected from natural habitats. They are usually restricted to polluted areas, including mining and post-mining areas (Samecka-Cymerman and Kempers, 2001, Anawar et al., 2006, Jana et al., 2012, Peng et al., 2018), industrial areas (Moreira et al., 2011) or stormwater catchment areas (Fritioff and Greger, 2003).

One of the most often reported examples of the use of J. effusus for phytoremediation is the removal of metals from contaminated soils and wastewater in the mining and post-mining areas (Favas et al., 2012, Zhang et al., 2012). This can be explained not only by a high tolerance of this species to high metal concentrations in soil, but also by its ability to thrive at extremely low pH of the growing media. Soils in mining areas are often affected by acid mine drainage originating from the weathering of pyrite and, to much lesser extent, of other metal sulfides (Migaszewski et al., 2008). J. effusus can tolerate pH as low as 2.1 (Fyson, 2000). Notwithstanding a long interest in the studies of element uptake and accumulation by J. effusus, still little is known about a typical content of such elements as silver and rare earth elements in samples of this species collected from natural habitats.

This study aimed at comparison of trace element and rare earth element concentrations in samples collected seasonally (four times per vegetative season) from three distinct locations characterized by a different land use. The main objectives of this study are to: (i) compare concentrations of trace elements in shoot with those in root and soil in order to describe accumulation and translocation of each element in J. effusus; (ii) check whether seasonal differences in element concentrations have the same pattern in all investigation sites; and (iii) find potential North American Composite Shale (NASC)-normalized rare earth element concentration anomalies in the examined samples.