Avaliação do efeito combinado de luz e temperatura nas respostas ecofisiológicas de cepas de Cylindrospermopsis racibiorskii

Abstract

The blooms of potentially toxic cyanobacteria represent one of the main effects of eutrophication. Among the bloom forming species stands out Cylindrospermopsis raciborskii whose success has been attributed to their phenotypic plasticity and high tolerance to environmental factors such as low light availability. Despite the factors that explain the dominance of cyanobacteria have been the subject of many studies, our present knowledge is still far from a comprehensive theory that explain the causes, occurrence and control of blooms. Most ecophysiological studies examined C. raciborskii response to individual factors, but more information is needed about the combined effects of variables (eg temperature and light) to improve our interpretation of distribution in different niches of the same environment. In this context, the objective of this study was to investigate the influence of the combined effect of light and temperature in the ecophysiological responses of three strains of C. raciborskii (Cylindro 1, 2 and 3), isolated from the reservoir Camorim (RJ), a naturally eutrophic system. To determine the effect of light intensity and temperature on growth and different ecological characteristics related to light use (EK - light intensity of photosynthesis saturation rETRmax - maximum rate for electron transport, α photosynthetic efficiency and Rmax - maximum yield of the cultive), studies of cultivation in laboratory were combined six light intensities (10, 40, 60, 100, 150 and 500 μmol m-2 s-1) and four temperatures (15, 20, 25 and 30°C). The highest growth rates were observed when combining temperatures above 20°C with high light intensities, and Cylindro 1 grew more slowly than the other two strains. All three strains had reduced Rmax in highest light intensity and temperature tested. The parameters related to the photosynthetic capacity (rETRmax, EK and α) of the three strains were sensitive to temperature, there is also the influence of light intensity. Above 20°C temperatures, combined with high light intensity, negatively affected the maximum relative rate of electron transport (rERTmax). The values indicated that EK Cylindro 1 can be considered as adapted to high light intensity Cylindro while strains 2 and 3 are adapted to low light, such request by lower irradiance. Strains under limitation or light saturation were influenced by temperature, confirming the interaction of these two factors. The strains in this study confirmed the intraspecific variability of C. raciborskii and suggest the existence of different populations of this species in different niches of the same environment, which would be a favorable factor for algal blooms extension of C. raciborskii and explain the frequency of occurrence and distribution of this species around the world