Response of Cyanobacterial Photosynthetic Rate to Different Conditions of Pulsed Light

In this paper, pulsed light (red light, 625 nm) with different parameters were set to study the response of cyanobacterial photosynthetic rate to pulse frequency, intensity, and duty ratio by using the oxygen electrode, in order to achieve optimized light mode for high-efficiency cultivation of microalgae. The results showed that pulsed light with high frequency and small-duty ratio could alleviate photoinhibition under high light stress and achieve similar even higher photosynthetic rate compared to continuous light with the same peak intensity. Photosynthetic rate of cyanobacteria under the same intensity and duty ratio rose with the increase of frequency and reached a relatively stable high level when the frequency went above 100 Hz. Interestingly, under the condition of 2100-µmol photon m−2 s−1 peak intensity, 33% duty ratio, and 200 Hz, the photosynthetic rate was 1.13 times that under continuous light (2100 µmol photon m−2 s−1), saving nearly 67% of the input light energy and improving the conversion rate of light energy by 3.4 times. Mechanisms of pulsed light effect are also analyzed, based on the consumption and accumulation of intermediate substance. The conclusion of this study plays a positive role in reducing the operating cost of algal cultivation by the photobioreactor and even provides a new idea in the microalgal growth under outdoor stress conditions.