# Functional Traits of Plant Species Suitable for Revegetation of Landfill Waste from Nickel Smelter
## 1 Introduction  
Industrial activities leave unwanted traces in the surrounding territory and have a severe impact on the environment. As is well known, industrial and mining wastes with a high content of heavy metals pose a risk to the environment and have a demonstrable toxic effect on vegetation and soil microorganisms and their life processes [1; 2; 3]. These environmental burdens represent a very negative factor influencing the functional spatial structure of the landscape. There is not only contaminated groundwater around the landfill but also a high level of air pollution with toxic dust. [4]. Recently, various methods have been used worldwide for the remediation of similarly contaminated sites: isolation and stabilization of geochemically transformed elements [5; 6; 7], using natural alkaline material [8], covering of mine tailings by using inert materials [9], soil washing [10], electrokinetic remediation [11], microbiological methods [12] and many others. These technologies can be successful but generally require several specific processes, which take a long time. They are often expensive and can be practically used only in small areas [13]. Therefore, there is currently an increasing emphasis on the use of various phytotechnologies, including phytoextraction, phytodegradation, rhizfiltration, phytostabilization, phytovolatilization or phytocapping [1; 14; 15; 13]. Revegetation is a low-cost measure based on the use of naturally occurring plants to cover mining sites to not allow a release of heavy metals from mining waste into surrounding soil, groundwater and air by creating natural surface biomass layer as well as a branched root system. Thanks to this plant cover, water and wind erosion are also prevented, rhizosphere properties can be improved and thus the landfill can be gradually revitalized [13].  
The investigated site was the landfill waste of black mud near the town of Sered' (SW Slovakia), which is a source of heavy metal contamination. The landfill environment is unfavourable for plant growth. Landfill material is not soil in the real sense; it is industrial waste that has poor physical properties without developed soil structure. Due to its black colour, the landfill surface heats up and dries out very quickly. The material is strongly alkaline (pH 8.5) and the organic content is very low 0.05%. The C:N ratio is 0.74:0.05. Total content of Fe\({}_{2}\)O\({}_{3}\) is 78% and Al\({}_{2}\)O\({}_{3}\) 3.27%. Content of chromium is the highest 24,300 mg/kg, nickel 2920 mg/kg, zinc 300 mg/kg and copper 79 mg/kg. [16]. It does not contain enough biogenic elements for the proper plant growth and nutrition. Greening of the landfill waste can be considered as one of the most natural, and in this case, the most appropriate remediation methods.  
This work was aimed to characterise native plant species that have been able to adapt in an extreme environment unfavourable for plant growth. The functional traits of three plant species _Populus alba_, _Calamagrostis epigejos_ and _Diplotaxis muralis_ were evaluated, which reflect the plant's response to the habitat and a way of adapting to environmental conditions.