Phytohormones enhanced carbon fixation and biomass production in CO2 absorption-microalgae conversion system under light stress

CO2 absorption-microalgae conversion (CAMC) system can be a sustainable technology to achieve low-energy carbon capture and resource utilization in response to zero carbon. However, light stress could restrict the carbon utilization efficiency of CAMC system. In this study, melatonin (MT) and indole-propionic acid (IPA) as phytohormones, were used to promote the carbon fixation capacity and biomass yield of CAMC system under light stress, and the potential mechanism was also discussed. Both MT and IPA promoted the growth of Spirulina, and 10 mg-MT group obtained the highest biomass and carbon fixation capacity, which were 27.61 % and 30.62 % higher than control. MT and IPA promoted the activity of superoxide dismutase (SOD), catalase (CAT), and glutathione reductase (GR), enhancing antioxidant activity to avoid oxidative damage. The results of transmission electron microscopy (TEM) and cell apoptosis showed MT and IPA reduced cell membrane damage and apoptosis. Phytohormones induced the carbon flux flow to the synthesis of carbohydrate and protein, and increased carbohydrate and protein productivity. Moreover, the maximum phycocyanin content and yield were 13.74 % and 43.25 % higher than the control. Therefore, adding phytohormones was an effective strategy to achieve high-value bioresources of microalgae in CAMC system under light stress.