Passive leakage dominates cadmium-induced release of dissolved extracellular organic matters from Chlorella vulgaris

The production of microalgal dissolved extracellular organic matter (dEOM) is environmentally significant, yet the mechanism of its release under heavy metal stress remains unclear. In this study, Chlorella vulgaris dEOM production was quantitatively analyzed under 0-25 mg/L Cd²⁺ exposure across exponential-stationary phases. The results identified passive leakage as the dominant release mechanism across varying Cd²⁺ levels, primarily stemming from: (1) cell division processes during exponential growth under both low and high stress, and (2) membrane damage under high stress from exponential to stationary phase. Biomarker analysis-including changes in cell composition, reactive oxygen species, antioxidant levels, and malondialdehyde-provided mechanistic support for passive leakage. Conversely, active excretion showed no correlation with biomarker patterns, suggesting it contributed minimally to dEOM production. ​​These findings establish passive leakage as the primary driver of microalgal dEOM release under Cd²⁺ stress, providing novel crucial insights for understanding organic matter production in aquatic systems.​.