Growth of the aquatic macrophyte Ricciocarpos natans (L.) Corda in different temperatures and in distinct concentrations of aluminum and manganese.

One of the consequences of global mining is the exposure of metals into the environment, caused by the rupture of tailings dams. Excess of metals, such as aluminum (Al) and manganese (Mn) can cause serious damage to fauna and flora. The presence of these metals, associated with the temperature increase that occurs nowadays can potentially increase biochemical and metabolic rates in plant tissues and may affect growth. Therefore, the objective of this work was to evaluate the toxicity of the metals Al and Mn into the biomass' growth of the macrophyte Ricciocarpos natans, under two temperatures (25 and 27 °C). R. natans individuals (n = 10 ± 0.5 cm wide) were exposed during 30 days to Al (1.5; 2.5 and 5.0 mg L-1) and Mn (0.7; 1.5 and 3.0 mg L-1) at temperatures and photoperiod-controlled germination chambers. Fresh macrophyte masses were determined gravimetrically to determine the kinetic growth using a logistic model. With that, it was noticed that the presence of Al interfered negatively in the increase of the R. natans biomass, mainly in the highest concentrations and at 27 °C. Mn, on the other hand, affected the increase in biomass, mainly in the highest concentration. As a result, the growth coefficients (μ) changed, being up to 4 times lower in the Al bioassays and up to 2 times higher than the control in the Mn bioassays. However, the dry R. natans biomass individuals that were exposed to the treatments was reduced when compared to the control, except for the lower concentration of Mn. These results contribute to the understanding of the environmental changes that can occur due to metals contained in mining tailings in aquatic ecosystems and the influence of global warming on the metabolic processes of the growth of aquatic macrophytes.