The effect of light availability on the photosynthetic activity and productivity of outdoor cultures of Arthrospira platensis (Spirulina)

The basic requirement for establishing economically viable large-scale production of algal biomass, be it for food, feed, high-value product, or energy, is the ability to produce the biomass at a low price. To achieve this goal, an efficient production protocol is needed that ensures that the potential productivity is obtained at any given time. When productivity is defined by the ability to utilize the available solar radiation that drives photosynthesis, the production protocol must be optimized to meet this requirement. In the current study, we demonstrate that by modifying the light available to Arthrospira platensis cells cultured outdoors by a variety of options like modifying the standing biomass concentration, changing the mixing rate, or shading can change the potential photosynthetic activity and apparent activity. By optimizing the light available to algae cells under outdoor conditions, productivity can be increased by approximately 50 %, from 15.6 g m^-2 day^-1 in a culture that suffers from overexposure to light to 22.4 g m^-2 day^-1 in a culture in which light downregulation is minimized. Therefore, by using a variety of methodologies to estimate photosynthetic activity, we demonstrate that overexposing the cells to light may result in downregulation of the photosynthetic activity leading to photoinhibition and lower biomass productivity.