Moderate calcium stress improves antioxidant phytochemical quality of Phedimus aizoon L. through flavonoid and glutathione dual ROS–Ca²+ detoxification strategy

Background Elevated soil calcium in karst regions significantly influences plant development and phytochemical composition. This study aimed to elucidate the physiological and molecular basis of high-calcium adaptation in P. aizoon and to evaluate the effects of exogenous calcium on its edible and medicinal quality. Methods P. aizoon seedlings were cultivated under five CaCl 2 concentration treatments. Growth responses, assessed by plant height and crown width, were used to identify three representative treatment groups for further analyses. Edible tissues from these plants were subsequently subjected to nutritional assessment, stress-related physiological measurements, antioxidant and hypoglycaemic activity assays, and metabolic and transcriptional profiling. Results P. aizoon exhibited a clear biphasic response to calcium gradients. Moderate calcium (30 mM) optimized growth performance and significantly enhanced the accumulation of total flavonoids (1.51-fold), polyphenols, and glutathione (GSH), together with elevated activities of antioxidant enzymes (SOD, CAT, GST, and APX). In contrast, severe calcium stress (150 mM) suppressed biomass accumulation while maintaining high antioxidant capacity. Multi-omics analyses indicated that calcium-responsive changes in flavonoid and glutathione metabolism were associated with the induction of stress-responsive transcription factors, including members of the MYB and WRKY families. Conclusion These findings suggest that P. aizoon adjusts growth and antioxidant metabolism across a calcium gradient through coordinated transcriptional and metabolic reprogramming. Enhanced flavonoid and glutathione metabolism may contribute to redox homeostasis under elevated calcium conditions. This study provides a conceptual framework for understanding plant responses to high-calcium environments.