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.

Response of Natural Cyanobacteria and Algae Assemblages to a Nutrient Pulse and Elevated Temperature

“…In a comparable set-up with water from one urban pond, negative growth rates were found for eukaryote phytoplankton, but not for cyanobacteria indicating that the algae suffered more from grazing by zooplankton than the cyanobacteria did ( Lürling et al, 2017 ). Hence, both the results of that study and our current study point toward a beneficial effect of warming on cyanobacteria, which most likely runs through competitive advantages in nutrient acquisition and grazing resistance (e.g., Tilman et al, 1982 ; Sterner, 1989a ; Yoshida et al, 2007 ; Ger et al, 2016 ; Lürling et al, 2017 ). Since in general biological rates are higher at warmer temperatures, including zooplankton grazing and respiration rates ( Moore et al, 1996 ), also zooplankton-mediated nutrient recycling ( Sterner, 1989b ) could stimulate grazing resistant cyanobacteria more at elevated temperature.…”

“…Growth rates may differ between monocultures and mixed species cultures due to competitive, allelopathic interactions ( Marinho et al, 2013 ; Torres et al, 2016 ), whereas selective grazing straightforwardly may suppress phytoplankton vulnerable to grazing, whilst facilitating grazing resistant phytoplankton ( Ger et al, 2014 , 2016 ). We incubated relatively small volumes of water, which could make the presence of large-bodied grazers a rather stochastic event; however, visual inspections did not yield any large bodied cladocerans present in the experimental units.…”

Unusual cohabitation and competition between Planktothrix rubescens and Microcystis sp. (cyanobacteria) in a subtropical reservoir (Hammam Debagh) located in Algeria

“…due to the lack of data on this variable. A recent paper of Torres et al [ 48 ] on the effect if light on the competition between Microcystis aeruginosa and Planktothrix agardhii showed that M . aeruginosa is a better competitor for light than was previously thought and that this species is able to dominate even in low-light conditions.…”

Effect of Increased Temperature on Native and Alien Nuisance Cyanobacteria from Temperate Lakes: An Experimental Approach

“…Experimental treatments were maintained in a modified MWC medium [ 66 ] under a 16:8 light:dark regime and light intensity of approximately 90 µmol m −2 s −1 . Illumination intensity was chosen according to a given preference for native P. agardhii [ 68 ] and A. gracile [ 44 ] growth. Cultures were grown in triplicate in 100 mL Erlenmeyer flasks.…”