微藻闪光效应发生的光照特征、生理基础及其环境调控的研究

Microalgae are huge group of photo-autotrophic plankton with many of which are attracting candidates for producing high value bio-actives. Liquid biofuel production with microalgae is considered as a sustainable method to alleviate the energy crisis as well as environment deterioration. However, the biomass yields for the conventional cultivation methods, i.e. open pond and closed photobioreactors, were much lower than the expected value and this has been a major bottleneck for the further improvement of the microalgal biofuel industry. According to the basic theories of photosynthesis, illuminating with intermittent light should be a feasible strategy to increase the photosynthetic efficiency as well as biomass yield (flashing light effect). However, due to the movement and self-shading effects, the light environments for the algal cell in aqueous suspended cultivation methods are largely unpredictable and so that the relationships between intermittent light and photosynthetic efficiency are unclear and inconsistent according to the current reports. In this research, a newly developed semi-dry attached cultivation system will be adopted to study the flashing light effect. With this attached cultivation system, the movements of the algal cell will be greatly reduced and so that the light environment is simply determined by the light source solely. The relationships between light usage efficiency and the parameters of intermittent light, i.e. frequency and duty cycle will be revealed by studying the growth under intermittent light. And by adopting proper statistical analyses, the accurate frequency and duty cycle ranges will be determined. At the same time, for the sake of actual applying of this flashing light effect, the possibilities and strategies to slow down the frequencies without deteriorating the efficiency will also be explored under different environmental pre-treatment including high light intensity, nitrogen deficiency, CO2 enrichment and salt stress. Finally, the photosynthesis characters of microalga biofilms that experienced typical intermittent light treatments will also be studied, so that the physiological basis of commencement as well as regulation of flashing light effect will be reveal. The results of this research would greatly clarify the long time existed ambiguous and controversies about the time scale of flashing light effect, would deepen the understanding on the photosynthesis process of microalgae, and would provide guidelines for the design of new generation of high efficient semi-dry attached cultivation system for microalgae.

生物量产率低是微藻资源规模化利用的瓶颈问题。闪光效应有提高微藻光能利用效率、增加生物量产率的巨大潜力，但其发生的频率和占空比等关键参数仍不清楚。现有的相关研究多基于传统悬浮培养体系，其结论因微藻自身光环境的多变而无法统一。本项目利用新近发展起来的半干贴壁培养技术，以产油微藻栅藻为对象，在藻细胞位置基本固定的情况下，通过研究不同频率、不同占空比的明-暗间歇光照下微藻光能利用效率，从而比较准确的定量微藻闪光效应发生的条件。在此基础上，首次探讨通过环境胁迫预处理的方法人为调控微藻闪光效应时间尺度的可行性。并通过研究典型明-暗间歇光照对微藻光合作用的影响，揭示闪光效应的发生和被调控的生理生化基础。上述研究将有助于澄清长期以来存在的关于微藻闪光效应的模糊认识、加深人们对微藻光合作用特点的理解，并为将闪光效应应用于微藻规模培养奠定理论基础。

微藻在高附加值农业、碳减排、可再生能源等方面有重要潜力。但是实际规模培养过程微藻生物量产率较低，限制了其产业化、规模化利用。利用明暗间歇光照能有效有提高微藻光能利用效率（所谓“闪光效应”），但“闪光效应”发生的频率和占空比等关键参数仍不清楚。本研究首次定量研究了贴壁条件下微藻发生闪光效应的频率范围，结果显示在明暗照光频率高于1Hz时发生闪光效应，但是发生全等效闪光效应的频率随着瞬时光强的升高而升高；当闪光频率较低（<0.1Hz）且占空比较低（<0.3）同时出现的情况下，光能利用效率急速降低，形成“效率陷阱”；当最高光强低于光饱和点的时候，微藻在一定频率的明-暗循环照光下的光能利用效率能够较连续弱光照射提高60%以上；明暗循环光照对光能利用效率的调节可能是作用于光合作用暗反应阶段，而不是光反应阶段。根据这些结果和结论，实践中设计贴壁式反应器的时候首先要尽可能的增大稀释倍数，并利用弱光下的明暗光照提高生物量产量；其次，明暗光照频率要尽可能高，这样才能避开低效率陷阱。