Influência de diferentes concentrações de níquel sobre o crescimento e desenvolvimento inicial de Guazuma ulmifolia Lam. (Malvaceae, Malvales)

Abstract

The irregular dumping of heavy metals in the environment is caused, most of the times, by mining activities. Among the metals processed by mining activities is the nickel, a chemical element which presents a great toxicity to fauna, flora and human beings. Aiming to avoid health damage to live beings caused by nickel, there is as an alternative: the soil decontamination through phytoremediation, technology, which uses plant species resistant to heavy metals and is able to extract, degrade, contain and or immobilize them in the soil. Therefore, this research goal was to evaluate the germination, growing and initial development of seeds and young plants of the Guazuma ulmifolia Lam species under different nickel concentrations, aiming its use in restoration of areas contaminated by this metal. So, the experiments were divided into two phases. In the first one, the G. ulmifolia seeds were distributed into six treatments with Ni (NO3)2 [C (0 mg.L-1), T1 (20 mg.L-1), T2 (40 mg.L-1), T3 (60 mg.L-1), T4 (80 mg.L-1) e T5 (100 mg.L-1)], with four repetitions per treatment and 20 seeds per repetition. In the second phase, it was used G. ulmifolia seedlings distributed into five treatments with Ni (NO3)2 [C (0 mg.L-1), T1 (100 mg.L-1), T2 (200 mg.L-1), T3 (400 mg.L-1) e T4 (600 mg.L-1)], each treatment was established with seven repetitions and each repetition was considered to be one seedling into a plastic container containing 1000 cm³ of substrate. At the end of the experiments, the obtained data were analyzed through the ANOVA test followed by the Tukey s multiple comparison test. The statistics results showed no significance to the germination and significant to root length and mortality after the G. ulmifolia germination which makes difficult the use of direct planting of its seeds in phytoremediation programs. Related to the established patterns for the seedlings, there was no significant difference in two of them (the collar diameter and the dry matter of the root) and the indication of significant difference within the others (height, number of leaves, dry matter of aerial parts, leaf area and nickel concentration in the soil after removing the seedlings). However, this difference does not disagree with the goals of phytoremediation, for the progress of all the seedlings was continuous. Moreover, results reveal a great potential of G. ulmifolia tolerance to high levels of nickel concentration, making itself promising in the phytoremediation of contaminated soils by nickel.