Specific growth rates vs. light exposure of Stephanodiscus neoastraea (diatom) and Planktothrix agardhii (cyanobacterium) were studied under different time regimes of illumination at 20 °C. Fluctuating irradiance simulating the transport of the algae within the aquatic light field by Langmuir circulations with a euphotic depth per mixing depth (z eu /z mix ) of 1 or 0.5 were compared with constant irradiance throughout the same photoperiod of 12 hours length as well as a photoperiod of 6 hours length. Fluctuating light (30 minutes for a cycle) resulted in a decrease of the maximum specific growth rates as compared with constant irradiance. The decrease amounted to 12 % for S. neoastraea and 30 % for P. agardhii at z eu /z mix of 1, and 46 % and 59 % at z eu /z mix of 0.5, respectively. The initial slopes of the growth vs. light exposure curves were also significantly decreased by light fluctuations. The photosynthesis vs. light curves of samples taken from cultures acclimated to saturating constant or fluctuating illumination simulating z eu /z mix of 1 showed no difference for P. agardhii but the maximum specific photosynthesis rate of S. neoastraea was increased by light fluctuations. Model calculations showed that the measured growth rates were reduced to a lesser extent than the calculated integrated photosynthesis, especially for the diatom. We suggest that the smaller effect of light fluctuations on the growth rate of the diatom is caused by more effective short-term acclimation mechanisms in diatoms compared to cyanobacteria.
No takes yet. Share an insight, caveat, or question.
Nicklisch et al. (2001) studied this question.