Nanoparticles (NPs) are an emerging tool for mitigating environmental stresses. Although beneficial roles of NPs have been reported in some plants, there is little data on magnesium (Mg)-NPs in alleviating drought stress. Therefore, the field experiment was conducted to study changes in biochemical attributes and essential oil (EO) compositions of yarrow (Achillea millefolium L.) plants under drought stress and Mg-NPs in 2016 and 2017. Irrigation regimes were used in two levels as well-watered (irrigation intervals of 7 days) and drought stress (irrigation intervals of 14 days) conditions, and Mg-NPs were sprayed on leaves in four levels (0, 0.1, 0.3, and 0.5 g L⁻¹). The results showed drought stress led to increased electrolyte leakage (EL), proline, carotenoid, anthocyanin, and total flavonoid content (TFC). However, flowers yield and EO yield were lower in plants exposed to drought stress as compared to well-watered conditions. The 0.3 and 0.5 g L⁻¹ Mg-NPs were more effective in alleviating drought stress by enhancing these traits. Heat map results showed that EL and TSS represented the high variability upon different treatments. The GC and GC/MS results represented that α-pinene (8.60–12.20%), 1,8-cineol (9.03–14.02%), camphor (6.84–9.80%), α-bisabolol (8.54–18.81%), chamazulene (14.23–22.50%), and caryophyllene oxide (7.20–9.80%) were the min EO constitutes of yarrow plants. Totally, drought decreased monopertens but increased sesquiterpenes of EO. To sum up, foliar applied Mg-NPs in a range of 0.3–0.5 g L⁻¹ can be recommended as effective tool to improve plant yield through changes in biochemical attributes of yarrow plants.

Zinc toxicity thresholds for reclamation plants are largely unknown. As a result, ecological risk assessments often rely on toxicity thresholds for agronomic species, which may differ from those of restoration species. Our objective was to provide Zn toxicity thresholds for forb species that are commonly used in reclamation activities. We used a greenhouse screening study where seedlings of yarrow (Achillea millefolium L.), Bigelow's tansyaster (Machaeranthera bigelovii (Gray) Greene var. bigelovii), blue flax (Linum perenne L. var. Appar), alfalfa (Medicago sativa L. var. Ladak), Palmer's penstemon (Penstemon palmeri Gray), and Rocky Mountain penstemon (Penstemon strictus Benth. var. Bandera) were grown in sand culture and exposed to increasing concentrations of Zn. Lethal concentrations (LC50 - substrate Zn concentration resulting in 50% mortality), effective concentrations (EC50 - substrate Zn concentration resulting in 50% biomass reduction), and phytotoxicity thresholds (PT50 - tissue Zn concentration resulting in 50% biomass reduction) were then determined. Phytotoxicity thresholds and effective concentrations for these reclamation species were relatively consistent between species. Our estimates of PT50-shoot for these species range from 1258 to 3214 mg Zn kg-¹ . Measures of EC50-plant for these restoration forbs ranged from 82 to 214 mg Zn L-¹ . These thresholds might be more useful for risk assessors working on reclamation sites than those based on non-reclamation species that are widely used.

This study evaluates bioaccumulation and translocation potentials of trace elements (TEs) by Saponaria officinalis L. (soapwort) and Achillea millefolium L. (yarrow) in order to select and optimize phytoremediation methods for the polluted environment of the city of Bor, Serbia. According to the enrichment factor for soil (i.e., 57.9–128.8 for Cd and As), pollution index (i.e., 6.6–84.7 for Cu), pollution load index (2.9–98.8), individual potential risk factors (11.5–5163), and potential ecological risk index values (260–6379), urban and rural soils from the city of Bor were classified as very contaminated with the investigated TEs. The results from all the indices and statistical analysis showed significant ecological risks of Cu, As, and Cd at the investigated sites and urge the need for remediation. The enrichment factor of the plants for As (566.3) and Cd (306.2) indicated a high enrichment level of the herb organs at all the sites. Since there are small differences in metal accumulation index values between the herbs and their parts (root, shoot), soapwort and yarrow can be considered as potential bioindicators. Based on the biological concentration and translocation factors, soapwort can be recommended as a suitable herb for phytoextraction purposes of Pb, As, and Cd polluted areas. Yarrow shows good characteristics for phytoextraction of Cu, Pb, and As from the contaminated soil. Principal component analysis (PCA) and hierarchical cluster analysis (HCA) results indicate their similar origin from atmospheric deposition. Therefore, these herbs can be utilized as a bioindicator and phytoremediator in polluted areas influenced by metallurgical activities to detect possible levels of TEs.

The aim of study was to determine the phytoextraction of rare earth elements (REEs) to roots, stems and leaves of five herbaceous plant species (Achillea millefolium L., Artemisia vulgaris L., Papaver rhoeas L., Taraxacum officinale AND Tripleurospermum inodorum), growing in four areas located in close proximity to a road with varied traffic intensity. Additionally, the relationship between road traffic intensity, REE concentration in soil and the content of these elements in plant organs was estimated. A. vulgaris and P. rhoeas were able to effectively transport REEs in their leaves, independently of area collection. The highest content of REEs was observed in P. rhoeas leaves and T. inodorum roots. Generally, HREEs were accumulated in P. rhoeas roots and leaves and also in the stems of T. inodorum and T. officinale, whereas LREEs were accumulated in T. inodorum roots and T. officinale stems. It is worth underlining that there was a clear relationship between road traffic intensity and REE, HREE and LREE concentration in soil. No positive correlation was found between the concentration of these elements in soil and their content in plants, with the exception of T. officinale. An effective transport of REEs from the root system to leaves was observed, what points to the possible ability of some of the tested plant species to remove REEs from soils near roads.