# Functional Traits of Plant Species Suitable for Revegetation of Landfill Waste from Nickel Smelter
## 4 Discussion
### Plant Utilisation in Landfill Remediation Strategies  
From the obtained data we could state that all plant species were able to be inhabited and grow in the landfill waste, while each species had a different life strategy and way to adapt to this habitat with extreme conditions. _Calamagrostis epigejos_ proved to be a plastic species, and in the selected habitat it was probably the best of all species for water shortages. _Dipidaxis muralis_ showed the best adaptation, mainly in terms of the specific leaf area, the dry matter content in the leaves but also values of the water saturation deficit. _Populus alba_, although in the juvenile stage and affected by the lack of substrate moisture, was also able to adapt, colonize and create populations in habitats with adverse conditions. All three species belong to the same ecological group in terms of salinity [41]. They are tolerant to the concentration of readily soluble salts, especially sulphates, chlorides and carbonates of sodium, potassium, calcium and magnesium. Despite the unfavourable conditions persisting in the landfill waste, all three species were able to create viable populations. Many plant species can accumulate heavy metals in their bodies and are therefore often sought after as indicators of contaminated areas or are used directly to revitalize and phytoextract heavy metals from soils [15]. Within the plant kingdom, about 500 species of higher plants are currently known to have hyperaccumulating properties [42]. Most of them can accumulate a specific element and can be used in phytoremediation methods. These species occur in 34 families, most of which belong to _Brassicaceae_ family [42, 43]. _Dipidaxis muralis_ belongs to the family _Brassicaceae_, and even though it is not referred to as a hyperaccumulator, this species proved its ability to adapt to the high content of heavy metals in the substrate. In addition, the plasticity of species _Populus alba_ and _Calamagrostis epigejos_ allows them to grow in contaminated sites. These species are able to tolerate high levels of contaminants in the soil and partially accumulate them in their tissues [33, 44]. Poplar is a sought-after species for the remediation of polluted sites due to its rapid growth, deep root system, large biomass production [45, 46]. This species is suitable for soil rhizodegradation and phytoextraction of Cd, Ni, Fe, Zn and Pb [33, 44, 47, 48]. [PERSON] et al. [49] have been working directly with _Calamagrostis epigejos_. They concluded that its properties such as adaptation mechanism, phenotypic plasticity, genotypic variability, low nutrient requirements support its spread in this type of site and predestines it to indicate soil pollution and possible phytoremediation of contaminated areas. Its ability to colonize landfills after mining activities [50] plays an essential role in not spreading contaminants into the environment and crops. The species is suitable for remediation of soils polluted with heavy metals [48]. Phytocapping, as one of the phytoremediation technologies, is a new ecofriendly and cost-effective method working with overlapping landfill wastes with green naturally occurring plants. The main advantage of phytoreapping is the reduction or complete stopping of heavy metal leaching into soil and groundwater. Plant biomass also slows down the spread of contaminants through the air and helps prevent erosion. Plants growing on landfill wastes are adapted to these conditions, and the concentration of heavy elements gradually decreases. Thanks to surface evaporation and plant transpiration, contaminated water is prevented from flowing down into the subsoil. Soil absorbs water and plants behave as \"pumps\" that can remove stored water [51, 52, 53]. The proposed phytoreapping procedures recommend the use of hyperaccumulators and especially as the first step it is recommended to create a layer on contaminated soil, which will create a suitable environment for the plant roots [13].