Most of the heavy metals (HMs), and metals/metalloids are released into the nature either by natural phenomenon or anthropogenic activities. Being sessile organisms, plants are constantly exposed to HMs in the environment. The metal non‐hyperaccumulating plants are susceptible to excess metal concentrations. They tend to sequester metals in their root vacuoles by forming complexes with metal ligands, as a detoxification strategy. In contrast, the metal‐hyperaccumulating plants have adaptive intrinsic regulatory mechanisms to hyperaccumulate or sequester excess amounts of HMs into their above‐ground tissues rather than accumulating them in roots. They have unique abilities to successfully carry out normal physiological functions without showing any visible stress symptoms unlike metal non‐hyperaccumulators. The unique abilities of accumulating excess metals in hyperaccumulators partly owes to constitutive overexpression of metal transporters and ability to quickly translocate HMs from root to shoot. Various metal ligands also play key roles in metal hyperaccumulating plants. These metal hyperaccumulating plants can be used in metal contaminated sites to clean‐up soils. Exploiting the knowledge of natural populations of metal hyperaccumulators complemented with cutting‐edge biotechnological tools can be useful in the future. The present review highlights the recent developments in physiological and molecular mechanisms of metal accumulation of hyperaccumulator plants in the lights of metal ligands and transporters. The contrasting mechanisms of metal accumulation between hyperaccumulators and non‐hyperaccumulators are thoroughly compared. Moreover, uses of different metal hyperaccumulators for phytoremediation purposes are also discussed in detail.

The impact of plant growth regulators (PGRs) “Stimpo” and “Regoplant” on Miscanthus x giganteus (Mxg) biomass parameters was investigated when the plant was grown in military soils with different properties from Dolyna, Ukraine and Hradcany, Czech Republic. The results showed that PGRs positively influenced the biomass parameters when the plant was grown in soil in Dolyna with good agricultural characteristics, the influence of “Regoplant” was higher and the best results were obtained with combined treatment: application to rhizomes before planting and spraying on the biomass during vegetation. Using of PGRs did not improve the biomass parameters when the plant was grown in poor soil in Hradcany. In parallel the peculiarities of the metals uptake process were studied for the following metals: chromium (Cr), manganese (Mn), nickel (Ni), copper (Cu), zinc (Zn), strontium (Sr) and lead (Pb). The uptake behavior of the monitored elements differed based on the soil quality. According to the bioconcentration factor uptake of the abiogenic elements, Cr and Pb, was dominant in the plant roots in both soils, whereas Ni was not detected in any plant tissues. The behavior of biogenic elements (Mn, Cu, Zn) and their analogs (Sr) was different. Those elements were more intensively taken up in shoot tissues in low-nutrient sandy Hradcany soils, while they were mainly taken up in plant roots in fertile Dolyna soils. The unusual behavior of biogenic elements in the low-nutrient soils may be explained by the effect of stress. However, more research is needed focused mainly on soil properties and nutrient availability in order to confirm or disprove this hypothesis and to explore the cause of the stress. The summarized results here show that soil properties influenced Mxg biomass parameters, affected the uptake behavior of metals significantly and tested PGRs cannot be utilized universally in the production of Mxg in the poor military soils.

Use of plant growth-promoting bacteria (PGPB) for cultivation of the biofuel crop Miscanthus × giganteus (Mxg) in post-military and post-mining sites is a promising approach for the bioremediation of soils contaminated by metals. In the present study, PGPB were isolated from contaminated soil and screened for tolerance against abiotic stresses caused by salinity, pH, temperature, and lead (Pb). Selected strains were further assessed and screened for plant growth-promoting attributes. The isolate showing the most potential, Bacillus altitudinis KP-14, was tested for enhancement of Mxg growth in contaminated soil under greenhouse conditions. It was found to be highly tolerant to diverse abiotic stresses, exhibiting tolerance to salinity (0–15%), pH (4–8), temperature (4–50 °C), and Pb (up to 1200 ppm). The association of B. altitudinis KP-14 with Mxg resulted in a significant (p ≤ 0.001) impact on biomass enhancement: the total shoot and dry root weights were significantly enhanced by 77.7% and 55.5%, respectively. The significant enhancement of Mxg biomass parameters by application of B. altitudinis KP-14 strongly supports the use of this strain as a biofertilizer for the improvement of plant growth in metal-contaminated soils.

Miscanthus x giganteus (Mxg) is a promising second-generation biofuel crop with high production of energetic biomass. Our aim was to determine the level of plant stress of Mxg grown in poor quality soils using non-invasive physiological parameters and to test whether the stress could be reduced by application of plant growth regulators (PGRs). Plant fitness was quantified by measuring of leaf fluorescence using 24 indexes to select the most suitable fluorescence indicators for quantification of this type of abiotic stress. Simultaneously, visible stress signs were observed on stems and leaves and differences in variants were revealed also by microscopy of leaf sections. Leaf fluorescence analysis, visual observation and changes of leaf anatomy revealed significant stress in all studied subjects compared to those cultivated in good quality soil. Besides commonly used Fv/Fm (potential photosynthetic efficiency) and P.I. (performance index), which showed very low sensitivity, we suggest other fluorescence parameters (like dissipation, DIo/RC) for revealing finer differences. We can conclude that measurement of leaf fluorescence is a suitable method for revealing stress affecting Mxg in poor soils. However, none of investigated parameters proved significant positive effect of PGRs on stress reduction. Therefore, direct improvement of soil quality by fertilization should be considered for stress reduction and improving the biomass quality in this type of soils.

Second-generation biofuel crop miscanthus is one of the most promising plants tested for phytomanagement of contaminated sites. In this preliminary pot case study, the most used hybrid Miscanthus x giganteus was cultivated in three different real contaminated soils: agricultural soil contaminated with Cd; post-military soil slightly contaminated with Zn, Pb and Cd; and soil contaminated by petroleum industry with metals and hydrocarbons. The stress response of plants and soil microbial communities was monitored to receive data that are important for successful phytomanagement application. With metals only, the plant grew well, and chlorophyll fluorescence measurement proved their good vitality. Changes in leaf anatomy (leaf thickness and sclerenchyma cells area) were additionally determined in post-military soil compared to agricultural. On the contrary, in petroleum-contaminated soil, the biomass yield was too reduced and also physiological parameters were significantly decreased. The response of microbial communities also differed. In agricultural soil, no microbial stress was determined. In post-military soil, it became reduced during the experiment, and in petroleum contamination, it increased year-on-year. It could be concluded that miscanthus is suitable for cultivation in metals contaminated soils with potential for microbial communities support, but in soil contaminated by the petroleum industry, its application did not seem meaningful.