Abstract This study describes the response of Arthrospira platensis to a variety of temperature conditions as reflected in variations of photosynthetic parameters, pigmentation, and biomass productivity in indoor photobioreactor (PBR) cultivations. These experiments are designed to better understand the impact of temperature, seasonal variations, and acclimation effects on outdoor biomass production. The irradiance level and temperature range (20 – 39°C) are chosen to enable modeling of semi-continuous operation of large-scale outdoor PBR deployments. Overall, the cultivations were quite stable with some pigment-related instabilities after prolonged high temperature exposure. Changes in productivity with temperature, as reflected in measured photosynthetic parameters, are immediate and mainly attributable to the temperature dependence of the photosaturation parameter, a secondary factor being variation in pigment content on a longer time scale corresponding to turnover of the culture population. Though pigment changes have minimum impact on productivity, prolonged exposure at 35°C and above yields a clear degradation in performance. Productivities in a semi-continuous operation are quantitatively reproduced with a productivity model incorporating photosynthetic parameters measured herein. This study confirms the importance of temperature for biomass and pigment production in Arthrospira cultivations and provides a basis for risk assessments related to temperature mitigation for large-scale outdoor cultivations. Keywords: Arthrospira Platensis, photosynthetic parameters, pigment production, productivity modeling, photobioreactors

his study describes the response of Arthrospira platensis to a variety of temperature conditions as reflected in variations of photosynthetic parameters, pigmentation, and biomass productivity in indoor photobioreactor (PBR) cultivations. These experiments are designed to better understand the impact of temperature, seasonal variations, and acclimation effects on outdoor biomass production. The irradiance levels and temperature range (20 – 39°C) are chosen to enable modeling of semi-continuous operation of large-scale outdoor PBR deployments. Overall, the cultivations were quite stable with some pigment-related instabilities after prolonged high temperature exposure. Changes in productivity with temperature, as reflected in measured photosynthetic parameters, are immediate and mainly attributable to the temperature dependence of the photosaturation parameter, a secondary factor being variation in pigment content. This study confirms that temperature is critical for optimal performance of Arthospira platensis for both biomass and pigment production and provides a basis for risk assessments related to temperature mitigation for large-scale outdoor cultivations. Finally, the biomass productivities in a semi-continuous operation mode are quantitatively reproduced with a productivity model incorporating the photosynthetic parameters measured herein. Those productivities are in good agreement with extensive outdoor testing in PBR arrays at large scale (24,000 L) and over long time periods (up to 18 months).