Photosynthetic characteristics of planktonic blue-green algae: The response of twenty strains grown under high and low light

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Abstract
The relationship between photosynthetic rate and irradiance was measured for 20 strains of blue-green algae from the genera Anabaena, Aphanizomenon and Oscillatoria. [Anabaena circinalis, A. flos-aquae, A. solitaria, A. spiroides, Aphanizomenon flos-aquae f. gracile, A. flos-aquae, O. agardhii, O. agardhii var. ixothrix, O. limnetica, O. redekei and O. rubescens]. Cells were grown at 20.degree. C under 6:18 light-dark at 30 or 150 .mu.E [einsteins] m-2 s-1. Under high light, the mean light saturated rate of photosynthesis (Pmax) of the Oscillatoria cultures was 14.8 mg O2 mg Chl [chlorophyll] a-1 h-1, but under low light this was depressed by 42%. Anabaena and Aphanizomenon cultures showed a similar mean Pmax under high light (13.8 mg O2 mg Chl a-1 h-1), but only a 13% depression of this value under low light. Oscillatoria cultures were more efficient than Anabaena and Aphanizomenon cultures at harvesting low irradiances, as measured by the initial slope of the photosynthesis-irradiance plot. The efficiency of light harvesting at low irradiances increased in Anabaena and Aphanizomenon cultures grown under low light. Oscillatoria cultures showed little increase in efficiency when grown under low light. Mainly due to the depression of Pmax, but also because of increased low light efficiency, the light saturation characteristic Ik was lower in low light cultures. In the Oscillatoria cultures, the mean Ik value decreased from 175 to 100 .mu.E m-2 s-1 and in the Anabaena and Aphanizomenon cultures from 215 to 164 .mu.E m-2 s-1. Probably due to the low short wavelength component of the light source used, little or no inhibition (mean 4.2%) of Pmax occurred even at irradiances > 700 .mu.E m-2 s-1.