Toxicidade comparada de metais pesados sobre características fisiológicas de sementes e plantas jovens de Hymenaea courbaril L.

Abstract

Anthropogenic activities related to increasing industrialization, mining, and, mainly, the use of agricultural inputs based on toxic chemical elements are intensifying environmental contamination due to the accelerated deposition of heavy metals. This situation causes impacts in different proportions to the biogeochemical cycles and their components, with emphasis on vegetation, soils, animals, and human beings. The development of techniques to decontaminate these components, in particular, the contaminated areas, becomes urgent. In the last decade, phytoremediation has been studied as one of the main techniques recommended to face this environmental problem. However, the use of plant species with the potential to remedy these environmental damages requires the understanding of defense mechanisms developed by plants, especially trees, which adequately remove, store, and survive the heavy metals present in contaminated soils. Thus, the objective of this dissertation was to evaluate the ecophysiological behavior of Hymenaea courbaril seeds and seedlings in response to the presence of heavy metals (copper, cadmium and lead). The study was carried out at the Laboratory of Plant Physiology and Biochemistry, at the National Institute of Amazonian Research, where the germination experiment was carried out with 50 seeds of H. courbaril destined for each treatment with the absence and presence of Cu, Cd and Pb. After germination, biometric variables and biomass production were measured. The experiment was carried out using a completely randomized design (DIC) with the establishment of four treatments: 1-) control - a quarter of the strength of Hoagland & Arnon, 2-) copper (Cu, 10 μM), 3- cadmium (Cd, 10 μM) e 4- lead (Pb, 5 μM), with fifty repetitions. The analysis of the experiment started from germination and ended in the seedling phase (90 days after germination), monitoring germination characteristics, growth, morphological (leaf and root), chlorophyll a, b and carotenoid contents, gas exchange, concentration of soluble sugars, starch, amino acids and proteins. Data were submitted to descriptive statistical analysis, analysis of variance (ANOVA) and Tukey's test of means (p<0.05) using R software, version 4.0.2. The results showed that H. courbaril can tolerate the studied Cd and Pb concentrations without causing significant damage to growth, biomass and photosynthetic apparatus. The species partially tolerated the toxic effects of Cu, showing a reduction in growth, biomass and physiology. Given the above, it is possible to state that H. courbaril tolerates stress by heavy metals during the initial phase of growth and development of seedlings and can be indicated for planting in areas contaminated by cadmium and lead and, due to the morphophysiological limitations presented by the species, partial tolerance of H. courbaril is attributed to the presence of copper.