Capabilities of alders (Alnus incana and A. glutinosa) to grow in metal-contaminated soil

This study examined the effects of metal-polluted soil on growth, biomass and uptake of trace metals and nutrients in Alnus incana and A. glutinosa seedlings. The rate of nitrogen fixation, counts of microbial groups, activities of phosphomonoesterases, and phenolic compounds in soil were also determined. Seedlings of various origin were grown for 158 days in forest soil (control) and in soil from a copper smelter area, with low nutrient content and high concentrations of Cu (1510 mg kg−1) and Pb (490 mg kg−1). Both alder species accumulated in their roots Cu and stored Pb, Zn (A. incana ≈ A. glutinosa) and Cd (A. glutinosa > A. incana). Concentrations of Cu, Pb, Zn and Cd were lower in shoots than in roots. Concentrations of Cu, Zn, Cd and Pb in leaves of both alder species were within normal ranges. Nutrient weight proportions P:K:Ca:Mg (N = 100) for leaves of Alnus spp. growing in polluted soil were higher than in the control. Alder growth in polluted soil was characterized by slight changes in total biomass of seedlings and nodules. Nodules stored Cu, Cd (A. incana > A. glutinosa), Pb and Zn, while concentrations of P and Ca were lower in nodules than in the control. N levels in leaves of alders grown in polluted soil were generally lower than those of alders grown in control soils. We also recorded a reduction in the rate of N2 fixation in nodules when alders were grown in polluted soil. In the rhizosphere in polluted soil, actinobacteria (actinomycetes) and copiotrophs were less numerous, while oligotrophs were more numerous. Also activities of phosphomonoesterases were strongly reduced, while concentrations of water-soluble phenols increased. The results suggest that both species of Alnus grow well in heavily polluted soil, in spite of accumulation of toxic metals in their roots and nodules and a decreased rate of N2 fixation.