| Abstract: |
Freshwater algae are the principal primary producers of lentic and lotic ecosystems, and their productivity is increasingly threatened by environmental stressors driven by anthropogenic activity and climate change. This empirical study investigated the biochemical adaptations of the freshwater green microalgae Chlorella vulgaris and Scenedesmus obliquus, together with the cyanobacterium Anabaena variabilis, exposed for twelve days to thermal stress (35 °C), salinity (100 mM NaCl), cadmium toxicity (10 µM CdCl2) and nutrient starvation [1]. Growth in terms of dry biomass and specific growth rate, photosynthetic pigments, stress biomarkers such as proline, soluble sugars and malondialdehyde, and the activities of superoxide dismutase, catalase, ascorbate peroxidase and glutathione reductase were quantified at the end of the exposure period. All stress treatments significantly reduced biomass accumulation, with cadmium imposing the strongest inhibition of 58.2 percent, whereas proline, soluble sugars, malondialdehyde and all four antioxidant enzymes increased markedly and chlorophyll content declined. Pearson correlation analysis revealed strong negative associations between chlorophyll a and every stress marker and strong positive associations among the antioxidant enzymes, proline and malondialdehyde [2]. All changes were statistically significant at p < 0.05, and the magnitude of each response scaled with stress severity. The results demonstrate a coordinated, severity-dependent biochemical defence system in which antioxidant up-regulation and osmolyte accumulation confer partial tolerance to multiple stressors. The findings provide quantitative evidence that biochemical markers can serve as early-warning indicators of environmental stress in freshwater ecosystems and support the use of such traits in biomonitoring and in the stress-based enhancement of algal biomass for biotechnology [3]. |
