Efeitos da disponibilidade de luz e limitação de nutrientes sobre a competição entre cepas de Cylindrospermopsis raciborskii e Microcystis aeruginosa

Abstract

The increase in occurrence and dominance of the cyanobacteria Cylindrospermopsis raciborskii in freshwater ecosystems, observed worldwide, has resulted, in many cases, in a replacement of other species like Microcystis aeruginosa. The factors related with this dominance are still unknown. The aim of this work was to evaluate the influence of light and nutrients in the competition between C. raciborskii and M. aeruginosa. Experiments with 4 strains (2 strains of C. raciborskii, 2 strains of M. aeruginosa) in unialgal cultures have been accomplished to determine the nitrogen (N) and phosphorus (P) uptake dynamics. Competitive abilities of the two species have been evaluated in mixed cultures under 3 light intensities (high, medium and low) and under N and P limitation. The 4 studied strains presented the same nutrient uptake dynamics, absorbing N and P quickly (ca. 24 hours) and similar growth rates, mean doubling time and maximum yield of the cultures. At competition experiments M. aeruginosa was dominant in P-limited and control conditions under high and medium light intensities. C. raciborskii strains presented different responses: one of them was dominant in all conditions under low light intensity and also N-limited condition under medium light intensity. The other was dominant only in the N-limited and control conditions under low light intensity. It’s then evident the influence of the availability of light and nutrients in the competition between C. raciborskii and M. aeruginosa, however, the responses rely on the strains and specific generalization should be carefully evaluated.