Metabolic Regulation in Scenedesmus quadricauda Cells Improved Antioxidant Capacity and Oxygen Release under Nitrous Oxide Stress

To improve the microalgal tolerance to nitrous oxide (N₂O) impurity in the flue gas of circulating fluidized bed boilers in power plants, metabolic pathways in Scenedesmus quadricauda cells were regulated to improve antioxidant capacity and oxygen release under N₂O stress. The biomass dry weight increased by 13.8% with a N₂O concentration of 80 ppm, which effectively increased the photosynthetic electron transfer efficiency and oxygen release rate. Superoxide dismutase activity in microalgal cells increased 2.21-fold, which significantly enhanced cellular antioxidant capacity. N₂O restricted glycolysis and the tricarboxylic acid cycle to synthesize more starch from intermediate products of photosynthetic carbon fixation, resulting in lower oxygen consumption in microalgal respiration. N₂O decreased the cellular carbon-to-nitrogen ratio and extracellular polymers, but expression of metabolites such as methyl gallate was upregulated to enhance cellular anti-inflammatory and antibacterial capacity. Chlorophyll fluorescence quenching was reduced with an N₂O concentration of 300 ppm, resulting in cellular photoinhibition and increased reactive oxygen species, which led to oxidative damage and a 1.45-fold increase in the malondialdehyde content.