Specific growth rate of Chlamydomonas reinhardtii and Chlorella sorokiniana under medium duration light dark cycles: 13-87 s

The specific growth rate of Chlamydomonas reinhardtii and Chlorella sorokin iana decreased under square-wave light/dark cycles of medium duration, 13-8 7 s, in comparison to continuous illumination. Three experiments were done in three different turbidostats at saturating and sub-saturating light inte nsities during the light period, 240-630 mu mol m(-2) s(-1). Within each ex periment the light intensity during the light periods of the intermittent l ight regimes was equal and this intensity was also applied under continuous illumination. The specific growth rate decreased proportional or more than proportional to the fraction of time the algae were exposed to light; this light fraction ranged from 0.32 to 0.88. We conclude that under these ligh t regimes the chlorophyta C. reinhardtii and C. sorokiniana are not able to store light energy in the light period to sustain growth in the dark perio d at the same rate as under continuous illumination, C. reinhardtii increas ed its specific light absorbing surface by increasing its chloropyll-a cont ent under light/dark cycles of 13 s duration and a light fraction of 0.67 a t 240 mu mol m(-2) s(-1); the chloropyll-a content was twice as high under intermittent illumination in comparison to continuous illumination. The com bination of a higher specific light absorption together with a lower specif ic growth rate led to a decrease of the yield of biomass on light energy un der intermittent illumination. (C) 1999 Elsevier Science B.V. All rights re served.