title: Assessment of the Effects of Light Availability on Growth and Competition Between Strains of Planktothrix agardhii and Microcystis aeruginosa.
abstract: In this study, we tested the hypothesis that Planktothrix agardhii strains isolated from a tropical water body were better competitors for light than Microcystis aeruginosa strains. These cyanobacteria are common in eutrophic systems, where light is one of the main drivers of phytoplankton, and Planktothrix is considered more shade-adapted and Microcystis more high-light tolerant. First, the effect of light intensities on growth was studied in batch cultures. Next, the minimum requirement of light (I*) and the effect of light limitation on the outcome of competition was investigated in chemostats. All strains showed similar growth at 10 μmol photons m(-2) s(-1), demonstrating the ability of the two species to grow in low light. The optimum light intensity was lower for P. agardhii, but at the highest light intensity, Microcystis strains reached higher biovolume, confirming that P. agardhii has higher sensitivity to high light. Nonetheless, P. agardhii grew in light intensities considered high (500 μmol photons m(-2) s(-1)) for this species. M. aeruginosa showed a higher carrying capacity in light-limited condition, but I* was similar between all the strains. Under light competition, Microcystis strains displaced P. agardhii and dominated. In two cases, there was competitive exclusion and in the other two P. agardhii managed to remain in the system with a low biovolume (≈15%). Our findings not only show that strains of P. agardhii can grow under higher light intensities than generally assumed but also that strains of M. aeruginosa are better competitors for light than supposed. These results help to understand the co-occurrence of these species in tropical environments and the dominance of M. aeruginosa even in low-light conditions.
authors.affiliation: Laboratório de Ecologia e Fisiologia do Fitoplâncton, Departamento de Biologia Vegetal, Universidade do Estado do Rio de Janeiro, Rua São Francisco Xavier 524 - PHLC Sala 511a, CEP 20550-900, Rio de Janeiro, Brazil.
authors.forename: Camila de Araujo
authors.initials: Cde A
authors.lastname: Torres
authors.affiliation: Aquatic Ecology and Water Quality Management Group, Department of Environmental Sciences, Wageningen University, Wageningen, The Netherlands.|Department of Aquatic Ecology, Netherlands Institute of Ecology (NIOO-KNAW), Wageningen, The Netherlands.
authors.forename: Miquel
authors.initials: M
authors.lastname: Lürling
authors.affiliation: Laboratório de Ecologia e Fisiologia do Fitoplâncton, Departamento de Biologia Vegetal, Universidade do Estado do Rio de Janeiro, Rua São Francisco Xavier 524 - PHLC Sala 511a, CEP 20550-900, Rio de Janeiro, Brazil. manzi.uerj@gmail.com.
authors.forename: Marcelo Manzi
authors.initials: MM
authors.lastname: Marinho
mesh_terms: D000458:Cyanobacteria / Q000254:growth & development* / Q000528:radiation effects*; D005618:Fresh Water / Q000382:microbiology; D008027:Light; D046931:Microcystis / Q000254:growth & development* / Q000528:radiation effects*; D010839:Phytoplankton / Q000254:growth & development / Q000528:radiation effects; D014871:Water Microbiology
keywords: Chemostats; Continuous culture; Cyanobacteria; Interspecific variability; Intraspecific variability; Light limitation