Objectives With the development of industrialization, the atmospheric concentration of greenhouse gases such as CO2 has consistently risen, and people are increasingly concerned about the resulting greenhouse effect and extreme weather events. In recent years, microalgae photosynthesis has been considered an effective means of CO2 fixation. In previous studies, we successfully isolated and cultured Chlorella ZY-1 for efficient CO2 fixation. Light is the only energy source for photosynthesis and is essential for microalgae. Algal cells through photosynthesis convert light energy into chemical energy for CO2 fixation and other activities. Different temperatures, culture medium initial pH, gas flow rate, and physical and chemical culture conditions were investigated.
Methods Too intense or too little light affects microalgae photosynthetic efficiency, growth and metabolism. In order to further improve Chlorella ZY-1 productivity and CO2 fixation, the optimum light intensities for Chlorella ZY-1 carbon sequestration and growth were studied, based on previous research results. The best culture conditions, light intensities, cycles and light sources for cultivating ZY-1 were studied, and the growth of ZY-1, solid carbon and chlorophyll content, nitrate reductase activity, antioxidant enzyme activity and malondialdehyde content were measured to determine the best light conditions for carbon sequestration and optimization of growth.
Results Results show under light conditions of 2500–7500 lux, Chlorella ZY-1 growth and carbon sequestration rate increased in line with increased light intensity, while Chlorella ZY-1 intracellular malondialdehyde content, nitrate reductase activity and antioxidant enzyme activity remained steady. Under a light intensity of 10 000 lux, growth and carbon sequestration were suppressed and intracellular malondialdehyde content, nitrate reductase activity and antioxidant enzyme activity increased. Chlorella ZY-1 light saturation values should be between 5000 and 7500 lux.
Conclusions Illumination time can promote the growth of Chlorella ZY-1 and carbon sequestration. When illumination time is extended, Chlorella ZY-1 intracellular malondialdehyde content, nitrate reductase activity and antioxidant enzyme activity do not appear to fluctuate, and intracellular photoinhibition does not occur. The best light cycle for Chlorella ZY-1 is 20 hours light/4 hours dark.
Acknowledgments This research was financially supported by the National Natural Science Foundation of China (Grant Nos. 51474128, 21506109 and 51204100).