Study on the Physiological Responses and Molecular Mechanisms of Antioxidant Stress in Chlorella pyrenoidosa under Various Sodium Salt Treatments

This study systematically investigated the effects of neutral salts (NaCl, Na2SO4), basic salts (Na2CO3, NaHCO3), and acidic salts (NaH2PO4, NaHSO4) on the growth, physiological responses, and molecular mechanisms of Chlorella pyrenoidosa. By measuring biomass, chlorophyll content, protein, lipid, and carbohydrate content, antioxidant enzyme activities (SOD, CAT, POD, MDA), as well as proline and soluble sugar levels in algal cells under varying salt concentrations, it was found that high salt concentrations generally inhibited microalgal growth. Among the salts tested, NaHSO4 and NaHCO3 exhibited the most pronounced inhibitory effects and induced severe oxidative stress. Na2SO4, on the other hand, suppressed photosynthesis primarily through elevated pH levels while simultaneously enhancing SOD activity. Transcriptomic analysis further revealed distinct gene expression patterns related to ion transport, pH regulation, and carbon metabolism under different salt stress conditions. This study elucidates, for the first time, the critical influence of anion type on salt stress responses, thereby providing a theoretical foundation for the development of microalgal strains with improved stress tolerance.