Adjusted Light and Dark Cycles Can Optimize Photosynthetic Efficiency in Algae Growing in Photobioreactors

Biofuels from algae are highly interesting as renewable energy sources to replace, at least partially, fossil fuels, but great research efforts are still needed to optimize growth parameters to develop competitive large-scale cultivation systems. One factor with a seminal influence on productivity is light availability. Light energy fully supports algal growth, but it leads to oxidative stress if illumination is in excess. In this work, the influence of light intensity on the growth and lipid productivity of Nannochloropsis salina was investigated in a flat-bed photobioreactor designed to minimize cells self-shading. The influence of various light intensities was studied with both continuous illumination and alternation of light and dark cycles at various frequencies, which mimic illumination variations in a photobioreactor due to mixing. Results show that Nannochloropsis can efficiently exploit even very intense light, provided that dark cycles occur to allow for re-oxidation of the electron transporters of the photosynthetic apparatus. If alternation of light and dark is not optimal, algae undergo radiation damage and photosynthetic productivity is greatly reduced. Our results demonstrate that, in a photobioreactor for the cultivation of algae, optimizing mixing is essential in order to ensure that the algae exploit light energy efficiently.藻类基生物燃料作为可部分替代化石燃料的可再生能源，具备极高的研究与应用价值，但当前仍需投入大量研究工作以优化培养参数，开发具备市场竞争力的规模化养殖体系。影响养殖产能的关键性因素之一为光照可及性。光能可充分支撑藻类生长，但光照过载时会引发氧化应激反应。本研究采用旨在降低细胞自身遮光效应的平板光生物反应器（flat-bed photobioreactor），探究了光照强度对盐生微拟球藻（Nannochloropsis salina）生长及脂质产率的影响。本研究分别设置连续光照与不同频率的光暗交替两种光照模式，以模拟光生物反应器内因搅拌产生的光照波动，进而探究不同光照强度的影响效果。研究结果显示，只要存在光暗周期以允许光合装置的电子转运体完成再氧化过程，盐生微拟球藻即可高效利用极强光照。若光暗交替模式未达最优，藻类将遭受辐射损伤，光合产能亦会大幅下降。本研究结果证实，在藻类养殖用光生物反应器中，优化搅拌操作是确保藻类高效利用光能的核心举措。