Acclimation of photosystem II in a cyanobacterium and a eukaryotic green alga to high and fluctuating photosynthetic photon flux densities, simulating light regimes induced by mixing in lakes

Abstract

SUMMARYPhotoacclimation of Scenedesmus protuberans F'ritsch and Microcystis aeruginosa Kutzing emend. Elenkin to high and fluctuating PPFD was studied in continuous cultures with computer-controlled variable light regimes. The aim of the work was to provide a better understanding of species-specific acclimation to high PPFD (as encountered by cyanobacteria in surface waterblooms), and of suppression of the growth of colony-forming cyanobacteria during periods of prolonged mixing in lakes. The dynamics of a set of variables was followed during the light period, including pigment composition, maximum rate, efficiency and minimum quantum requirement of photosynthesis, PS 11 cross-sections, and fluorescence variables. Both the green alga and the cyanobacterium displayed strong photo-inhibition of photosynthesis in the sinusoidal light regime, which simulated a natural light regime in the absence of mixing. P,,,,,^, a, QR and the ratio of variable to maximum fluorescence declined, and the number of inactive PS II centres and PS II,, centres increased towards midday. Introduction of oscillations in the diurnal light regime, simulating different intensities of wind-induced mixing in lakes, mitigated photo-inhibition. Microcystis showed a prompt non-photochemical quenching of fluorescence in all light regimes, even at low to moderate PPFD. The sustained presence of zeaxanthin in Microcystis possibly induced instant, thermal dissipation of excitation energy from the antenna. Microcyslis also exhibited a more reluctant acclimation to fluctuating PPFD. Growth rate of Scenedesmus was higher in all light regimes. This implied that if (known) differences in loss processes were ignored, Scenedesmus would outcompete Microcystis in lakes. Tbe results underlined the importance of buoyancy regulation in increasing the daily light dose of cyanobacteria (but at the same time preventing over-excitation), and ultimately in tbe success in Microcystis in stable lakes.

Artificial mixing to control cyanobacterial blooms: a review

“…Eukaryotic algae such as green algae and diatoms seem better adapted to these fluctuations (Flameling and Kromkamp 1997;Nicklisch 1998;Litchman 2000), while many cyanobacteria seem more sensitive. A study by Ibelings et al (1994) in laboratory cultures showed that the cyanobacterium Microcystis was more sensitive to changes in photon irradiance than the green alga Scenedesmus. In a field experiment, Mitrovic et al (2003) showed a decrease in Microcystis (but also of Scenedesmus) under fluctuating light, while the diatom Skeletonema was found to increase compared to static light conditions.…”

Comparison of the light‐limited growth of the nitrogen‐fixing cyanobacteria Anabaena and Aphanizomenon

“…In contrast to homogeneously distributed PPFRs in the dilute monoculture experiments, the cells in the dense competition experiment experienced a continuously changing PPFR upon circulation in the vessel. Generally speaking, there is no doubt that a fluctuating PPFR affects the growth of phototrophs (see, for example, Ibelings et al (1994) ; Schubert et al (1995)). If Aphanizomenon is less able to withstand such a dynamic light regime than Anabaena, this could explain the outcome of the competition experiment.…”

“…Chlorophyll a fluorescence measurements were made in situ at room temperature using the saturation-pulse method described by Schreiber, Schliwa & Bilger (1986), and the experimental setup described by Ibelings, Kroon & Mur (1994). A saturating pulse of light (12 000 µmol photons m −# s −" , 0n8 s), which induced maximal fluorescence (all PSII reaction centres closed), was administered at 15-min intervals.…”

Diurnal buoyancy changes of Microcystis in an artificially mixed storage reservoir

“…Reduction of growth of Microcystis in an artificially mixed lake has been described by Toetz (1981) . Not only will it no longer benefit from its buoyancy controlled vertical positioning, but Microcystis also showed a poor acclimation to light regimes simulating those induced by mixing in lakes (Ibelings et al ., 1994) .…”