Effects of light fluctuations on the growth and productivity of Antarctic diatoms in culture

Summary This work shows that the low division rates observed in diatoms in Antarctic waters seem to be due to conditions of irradiance rather than to the low temperature: low light intensity and light fluctuations are two factors which depress the division rate of diatoms. However, with regard to the productivity, Antarctic diatoms seem well-adapted to their turbulent environment. Cells grown in alternating periods of light and dark, notably a 2:2 regime which simulates conditions of vertical mixing, reach a higher rate of productivity than algae grown in continuous light. This difference may be due to the better use of light energy observed in the former group. In the Antarctic Ocean, which is characterized by frequent mixing of water masses, this increased efficiency of light utilization could be a way of adaptation, allowing the algae to overcome the restraints imposed by low light and low temperature, and to reach a higher productivity than expected. The low values of I_k and I_max as well as the absence of detectable photoinhibition indicate that Antarctic diatoms are capable to sustain their maximum primary production rate over a wide range or irradiance levels. On the other hand, the highest productivity in 2:2 regime shows that these species are more efficient when grown under fluctuating light. These results lead us to assume that the Antarctic species are well-adapted to live in the extreme conditions of light encountered in Antarctic Ocean: low irradiance and alternance of low and high light intensities.