The significance of selected tree species age in their efficiency in elements phytoextraction from wastes mixture

The phytoextraction of toxic elements present in industrial wastes by selected tree species seems to offer an interesting alternative to hyperaccumulators, which are generally highly effective but small. For this reason, the study aimed to compare the potential of 1- and 2-year-old Tilia cordata Miller and Ulmus laevis Pall seedlings growing on a mixture of wastes (flotation tailings and sewage sludges) in the environment. One-year-old T. cordata was the only plant unable to grow successfully. A general decrease in tree biomass was observed following their growth on the waste mixture. The mean biomass of 2-year-old T. cordata and U. laevis seedlings was 59.5 ± 1.6 and 57.0 ± 8.6 g, respectively, whereas that of 1-year-old T. cordata was 16.0 ± 9.3 g. These values were 46.2, 48.0 and 50.5% lower than those determined for the control trees. Phytoextraction of 67 elements in particular organs of trees in many cases was significantly diverse. According to the Friedman rank sum test, T. cordata (1y) and U. laevis (2y) growing in soil were the only plants that differed as regards their ability to phytoextract elements. In the case of trees growing on the waste mixture, the most effective accumulating plants were seedlings of 2-year-old T. cordata. Significantly lower efficiency was observed for 2-year-old U. laevis, while the lowest efficiency was recorded for 1-year-old T. cordata. The obtained results unambiguously pointed to the significant role of a proper selection of tree species concerning their age for phytoextraction of elements from polluted substrates.