Photosynthesis of Marine Algae in Fluctuating Light. I. Adjustment of Rate in Constant and Fluctuating Light Regimes

Abstract

The adjustment of photosynthetic rates to fluctuating and constant light was investigated in Hormosira banksii (Turn.) Dene., Carpophyllum maschalocarpum, (Turn.) Grev. and Ecklonia radiata (C. Ag.) J. Ag. by monitoring either CO2 exchange in emergent material with an infrared gas analyser (IRGA) or 02 exchange in submersed material with an 02 electrode. Using the IRGA, mean photosynthetic rates (P) in fluctuating light showed several kinetic patterns taking 2-4 h to become fully adjusted after pretreatments of low light or darkness. In continuous low light the adjustment period was similar but the pattern was less complex. The time for P to reach a steady value in fluctuating light can be substantially reduced by a 30 min pretreatment of the material in the higher light. Errors due to 02 storage in the bladders of Hormosira precluded study of the adjustment in immersed material of this species. In Ecklonia monitoring with an 02 electrode and microcomputer revealed adjustment periods of P to fluctuating light of at least 30-40 min. Classical induction contributes to the adjustments of P to fluctuating light but other processes such as post-illumination CO2 fixation and photoadaptive responses appear to play an important role. These long-term changes in photosynthesis complicate studies of photosynthesisirradiance responses. Capacity of these macroalgae to adjust photosynthetic performance may be significant for carbon gain in dynamic light. Key-words: Fluctuating light, photosynthetic rate adjustment, photosynthetic induction, marine algae, Hormosira, Ecklonia, Carpophyllum