Photosynthesis—Energy Relationships in Dunaliella

Published data on photosynthesis (P) – energy (E) relationships of Dunaliella cultures by various authors, and our unpublished data were modeled. Comparison of the P-E parameters showed that cell densities are to be considered to avoid bias in comparing different experiments. Three to four day acclimation of algal cultures to low (~42 μmol m⁻² s⁻¹) or high light energy (~144μmol m⁻² s⁻¹) levels is necessary for stabilization of cell pigments and to prevent any negative effects of culturing. Photosynthetic rates were maximum at temperatures around 26°C, N: P 28, neutral pH and 500 (μmol m⁻² s⁻¹) light energy. Over a 21 day period gross production decreased by about 7 fold while respiration decreased by 4 fold. Cultures grown at ~42 μmol m⁻² s⁻¹ or ~144 μmol m⁻² s⁻¹ showed a strong decrease in photosynthetic rate, rather than the respiration rate; as cells aged a marked decrease in photosynthesis: respiration resulted. The photosynthetic efficiency, carbon assimilation numbers and photosynthesis: respiration ratios of Dunaliella are of the same order of magnitude as those obtained on benign algae and toxigenic algae. In D. salina., acclimation to high light energy levels induced carotenoid production as protection from photoinhibition. For maximization of photosynthesis ammonia is the best nitrogen source. These findings have applications in mass cultivation of Dunaliella for commercial purposes.