Comparison of Cyanobacteria Phenotypes with Distinctive Photosynthetic Pigment Compositions to Simulated Lake Browning
Abstract
Browning of inland waters has been noted over large parts of the Northern hemisphere and is a phenomenon with both ecological and societal consequences. The increase in water color is generally ascribed to increasing concentrations of dissolved organic matter (cDOM) of terrestrial origin. Changes in water color will have profound effects on the phytoplankton composition in freshwater systems. Here, I examined the effect of changes in water color associated with coloured DOM (cDOM) on red and green phenotypes of the cyanobacterium, Pseudanabaena, which emerged to surface blooms in Dickson Lake (Algonquin Provincial Park, Ontario) in the summer of 2014. Results presented here indicated that: (A) the increased level of cDOM had little effect on the growth and photosynthetic activity of either phenotype when grown independently, suggesting that lake browning was a benign, rather than selective, ecological driver; and (B) neither phenotype achieved a competitive advantage when the two phenotypes were grown together under defined cDOM regimes suggesting coexistence of both phenotypes. These findings temper the ideas that, with climate change, only specific bloom forming cyanobacteria will prevail, as both phenotypes of Pseudanabaena were present and showed the ability to co-exist. Cyanobacteria of this genera are likely to thrive under warmer and browner conditions due to their photosynthetic pigment composition that allows them to capture light at a variety of wavelengths.