Physiological changes in carbon sequestration and lipid production characteristics of microalgae under high CO2 domestication.

Carbon dioxide utilization is a key component of carbon capture, utilization, and storage (CCUS) technology, with oil-producing microalgae-based carbon sequestration being particularly efficient. This study investigated the carbon sequestration potential and lipid metabolism of three marine microalgae (Chlorella sp., Isochrysis galbana, and Nannochloropsis oceanica) under CO2 concentrations ranging from 10% to 25%, covering typical industrial flue gas levels. The results showed that microalgae exhibited higher utilization efficiency at lower CO2 concentrations. Notably, Nannochloropsis oceanica demonstrated strong CO2 tolerance, maintaining a specific growth rate of 0.108 day⁻1 even at 25% CO2, with a biomass productivity of 0.03454 g·L⁻1·day⁻1-11.42% higher than Chlorella sp. and 7.23% higher than Isochrysis galbana. Under 10% CO2 conditions, its carbon sequestration efficiency and CO2 utilization rate reached 0.110 g CO2·L⁻1·day⁻1 and 2.15%, respectively, while Rubisco enzyme activity increased by 52.6%, indicating highly efficient carbon assimilation. Under 25% CO2 stimulation, the total lipid content of Nannochloropsis oceanica increased to 53.93%, surpassing Chlorella sp. (52.53%) and Isochrysis galbana (46.69%). The lipid profile showed 40.95% monounsaturated fatty acids and 28.82% eicosapentaenoic acid (EPA), demonstrating its potential for both bioenergy and high-value product development. This study systematically explores the growth lifecycle of microalgae under high CO2 environments, providing scientific insights into their carbon sequestration mechanisms and physiological responses, thereby offering valuable references for developing microalgae-based flue gas carbon sequestration technologies.