Effects of solar radiation on the photosynthetic activity of the red alga Corallina elongata Ellis et Soland

Abstract

The photoinhibition of photosynthesis was investigated in two morphotypes of the red alga Corallina elongata, i.e. sun and shade types, using pulse amplitude modulated (PAM) chlorophyll fluorescence and oxygen evolution. The contents of chlorophyll, phycoerythrin, phycocyanin and soluble protein were analysed. Exposure to solar radiation caused a strong decrease in the effective photosynthetic quantum yield. This decline was more pronounced in the shade than in the sun morphotype. The plants partially recovered from this effect, indicating that it was mainly due to reversible photoinhibition and, to a smaller extent, non-reversible photodamage. Photoinhibition occurred in this alga even in its natural habitat when the sun was at high angles. Recovery from photoinhibition was higher in algae grown in the sun than in the shade. The net photosynthetic oxygen production was higher in the shade than in the sun morphotype. A decrease in oxygen evolution was observed at about noon, recovering at dusk. The concentrations of chlorophyll a (Chl a) and phycoerythrin were higher in the shade than in the sun morphotype. The Chl a and phycocyanin contents did not change significantly throughout the day. However, a clear daily variation in phycoerythrin content was observed with a strong decrease around noon. The soluble protein concentration decreased around noon, but only in the sun morphotype. The relationship between the photosynthetic quantum yield, oxygen evolution and pigment concentration is discussed, together with photoinhibition.