Dynamic discrete model of flashing light effect in photosynthesis of microalgae

Abstract

For a photobioreactor for mass-culturing microalgae, it is known that flashing light effect enhances the efficiency of photosynthesis. A dynamic model for photosynthesis was developed to elucidate this effect. A particular feature of the model is that discrete RuBP particles circulate in the Calvin cycle and their speeds in the cycle are determined by the amount of ATP generated in the photon reception process. This can realise the light saturation under continuous light and the flashing light effect under fluctuating illumination. Laboratory experiments were conducted to obtain model parameters by curve-fitting for Chaetoceros calcitrans. The present model demonstrates the light flashing effect moderately well and elucidates its mechanism reasonably. Nomenclature ADP= adenosine diphosphate A R = normalised ATP amount consumed as a discrete RuBP particle circulates in the Calvin cycle ATP= adenosine triphosphate f = (T L + T D ) −1 = frequency of light-dark cycle (s −1 ) FLE = flashing light effect GAP = glycerinaldehyde-3-phosphate I = irradiance (µE m −2 s −1 ) k a = proportional ratio of normalised ATP amount to I n c = frequency of circulation of a discrete RuBP particle in the Calvin cycle when there is sufficient ATP (s −1 ) n R = number of discrete RuBP particles that bond CO 2 in the unit time,1 s P = photosynthesis productivity per cell expressed by the oxygen accumulation (fmol h −1 ) P c = generated oxygen as a discrete RuBP particle circulates in the Calvin cycle (fmol) PGA = phosphoglycerate RuBP = D-ribulose-1,5-bisphosphate T D = duration of dark period (s) T L = duration of light periods (s) = T L (T L + T D ) −1 = ratio of light period to dark period [ATP] = instantaneous dimensionless amount of ATP [RuBP] = instantaneous number of discrete RuBP particles in the Calvin cycle 208

The Enhancement of Photosynthesis by Fluctuating Light

“…This can realize the light saturation under continuous light and the flashing light effect under fluctuating illumination. Laboratory experiments were conducted on Chaetoceros calcitrans (Yoshimoto et al, 2005). All of the above lead us to the following conclusions: a.…”

“…Very fast alternations between high light intensities and darkness (from less than 40 μs to 1 s) can greatly enhance photosynthetic efficiency (Kok, 1953;Matthijs et al, 1996;Nedbal et al, 1996;Phillips & Myers, 1954;Terry, 1986). Such results have kindled research on their application in various photobioreactors and algal mass culture facilities aimed at the production of valuable carotenoids, lipids, and additional products of commercial interest, such as biodiesel and hydrogen Park et al, 2000;Terry, 1986;Yoshimoto et al, 2005). Several mechanisms were postulated to explain the enhancement effects of flashing light on photosynthesis.…”

“…Several mechanisms were postulated to explain the enhancement effects of flashing light on photosynthesis. It has been suggested that at high frequencies, there are non-linear effects related to the limited availability of quinone pool receptors under continuous high light (Kok et al, 1970), whereas other works hypothesized Rubisco particle circulation in turbulent flow (Yoshimoto et al, 2005), and mutual shading of algal cells thereby increasing the time they are exposed to optimal light (Park et al, 2000). The enhancement of photosynthesis by flashing light (both the rate and the efficiency) has been known for many years.…”

Design principles of photo‐bioreactors for cultivation of microalgae

“…Nevertheless, also cycles between 1 Hz and 1 kHz are very useful. The transition between slow cycles, where no storage effects occur and fast cycles with nearly complete integration has been described in [25]. Such fast mixing is accompanied by a high waste of mechanical energy and is therefore only likely to become a viable option in future reactor generations.…”

The technology of microalgal culturing

“…In microalgal cultures, mixing also affects the light regimen (Richmond 2000;Grobbelaar 2000). Fluctuations in light intensity faster than 1 s -1 enhance specific growth rates and productivities of microalgal cultures (Nedbal et al 1996;Ogbonna and Tanaka 2000;Janssen et al 2001;Yoshimoto et al 2005). In outdoor cultures exposed to photosynthetic photon flux densities above 1,000 lmol m -2 s -1 light exposure times should be as short as 10 ms to maintain high PE (Janssen et al 2001).…”