The role of an electron pool in algal photosynthesis during sub-second light–dark cycling

Abstract A key element to maximize photobioreactor (PBR) efficiency is the ability to predict microalgal growth and productivity depending on environmental conditions, out of which light availability is the most important one. As a result of mixing and light attenuation in a PBR, microalgae experience light–dark cycles that could enhance, or reduce, PBR productivity. The objective of this study was to develop and validate a mechanistic model that describes net specific photosynthetic oxygen production of Chlamydomonas reinhardtii under flashing light in the range of 100 to 1 Hz. The model is based on the biomass specific light absorption rate and the dissipation rate of excess absorbed photons. Net oxygen production is a direct measure of biomass growth. The model describes specific photosynthetic oxygen production based on the availability of reducing equivalents (electrons), which result from the light reactions. Electrons accumulate during the flash and serve as a pool for carbon dioxide fixation during the dark leading to partial or full light integration. Both, electron consumption and photon dissipation rates are based on a Monod-type kinetic relation. The underlying assumption of an electron pool appeared functional and its filling and emptying depended on the flash time. The simulations show that if the dark time between flashes is not sufficiently long the pool will not be completely emptied, and is responsible for a high energy dissipation rate and reduced photosynthesis. The measured net specific oxygen production rates are described well, but the description of the specific photon dissipation rate will need further investigation.