Nickel and zinc absorption and growth of Atlantic Forest trees cultivated in polluted soil

The Brazilian Atlantic Forest has been affected by the deposition of Ni and Zn, among other heavy metals adsorbed on atmospheric particles, which can be incorporated into the soil. If available in the soil, they can be absorbed by plant roots. The study aimed at testing experimentally the hypotheses: 1) Ni and Zn depositions increase their bioavailable fractions in the soil; 2) pioneer tree species absorb Ni and Zn from the soil in higher level and less growth changes than non-pioneer species. The experiment was carried out with six pioneer and non-pioneer species native to the Atlantic Forest, grown for 90 days in: soil with balanced fertilization (control) and in soil enriched with Ni, Zn or Ni + Zn. At the end, the concentrations of Ni and Zn were determined in four soil fractions (F1: soluble; F2: linked to oxides/hydroxides; F3: linked to organic matter: F4: residual metals) and in leaves, stems/branches and roots. Mobility factors in soil, concentration ratios between treatments and respective controls, translocation efficiency and relative growth rate in height, leaf number and total biomass were also calculated. The results showed that Ni and Zn concentrations increased significantly in the bioavailable soil fractions (F1, F2). The absolute content of Ni and Zn in the plants directly reflected the soil level in the available forms. Pioneer tree species absorb Ni and Zn in higher level and show less changes in growth than non-pioneer tree species.