Fluctuating Light (fluctuating + light)

Distribution by Scientific Domains


Selected Abstracts


Growth rates of phytoplankton under fluctuating light

FRESHWATER BIOLOGY, Issue 2 2000
Elena Litchman
Summary 1The effect of light fluctuations on the growth rates of four species of freshwater phytoplankton was investigated. Experimental light regimes included constant irradiance and fluctuations of a step function form, with equal proportion of high (maximum of 240 µmol photons m -2 s -1) and low light (minimum of 5 µmol photons m -2 s -1) (or dark) in a period. Fluctuations of 1, 8 and 24-h periods were imposed over several average irradiances (25, 50, 100 and 120 µmol photons m -2 s -1). 2Growth rate responses to fluctuations were species-specific and depended on both the average irradiance and the period of fluctuations. Fluctuations at low average irradiances slightly increased growth rate of the diatom Nitzschia sp. and depressed growth of the cyanobacterium Phormidium luridum and the green alga Sphaerocystis schroeteri compared to a constant irradiance. 3Fluctuations at higher average irradiance did not have a significant effect on the growth rates of Nitzschia sp. and Sphaerocystis schroeteri (fluctuations around saturating irradiances) and slightly increased the growth rates of the cyanobacteria Anabaena flos-aquae and Phormidium luridum (when irradiance fluctuated between limiting and inhibiting levels). 4In general, the effect of fluctuations tended to be greater when irradiance fluctuated between limiting and saturating or inhibiting levels of a species growth-irradiance curve compared to fluctuations within a single region of the curve. 5The growth rates of species under fluctuating light could not always be predicted from their growth-irradiance curves obtained under constant irradiance. When fluctuations occur between limiting and saturating or inhibiting irradiances for the alga and when the period of fluctuations is long (greater than 8 h), steady-state growth-irradiance curves may be insufficient to predict growth rates adequately. Consequently, additional data on physiological acclimation, such as changes in photosynthetic parameters, may be required for predictions under non-constant light supply in comparison to constant conditions. [source]


CYANOBACTERIAL ACCLIMATION TO RAPIDLY FLUCTUATING LIGHT IS CONSTRAINED BY INORGANIC CARBON STATUS,

JOURNAL OF PHYCOLOGY, Issue 4 2005
Tyler D. B. MacKenzie
Acclimation to rapidly fluctuating light, simulating shallow aquatic habitats, is altered depending on inorganic carbon (Ci) availability. Under steady light of 50 ,mol photons·m,2·s,1, the growth rate of Synechococcus elongatus PCC7942 was similar in cells grown in high Ci (4 mM) and low Ci (0.02 mM), with induced carbon concentrating mechanisms compensating for low Ci. Growth under fluctuating light of a 1-s period averaging 50 ,mol photons·m,2·s,1 caused a drop in growth rate of 28%±6% in high Ci cells and 38%±8% in low Ci cells. In high Ci cells under fluctuating light, the PSI/PSII ratio increased, the PSII absorption cross-section decreased, and the PSII turnover rate increased in a pattern similar to high-light acclimation. In low Ci cells under fluctuating light, the PSI/PSII ratio decreased, the PSII absorption cross-section decreased, and the PSII turnover remained slow. Electron transport rate was similar in high and low Ci cells but in both was lower under fluctuating than under steady light. After acclimation to a 1-s period fluctuating light, electron transport rate decreased under steady or long-period fluctuating light. We hypothesize that high Ci cells acclimated to exploit the bright phases of the fluctuating light, whereas low Ci cells enlarged their PSII pool to integrate the fluctuating light and dampen the variation of the electron flux into a rate-restricted Ci pool. Light response curves measured under steady light, widely used to predict photosynthetic rates, do not properly predict photosynthetic rates achieved under fluctuating light, and exploitation of fluctuating light is altered by Ci status. [source]