Impact of paraquat on allelopathic interactions between Chlorella sorokiniana and Lemna minor

The pervasive use of herbicides in aquatic environments has heightened the need to assess their specific effects on photosynthetic organisms such as microalgae and macrophytes. In freshwater ecosystems, species interactions, nutrient availability, and pollutants such as paraquat can significantly alter community dynamics. We investigated the effect of paraquat on allelopathic interactions between Chlorella sorokiniana and Lemna minor . In monocultures, C. sorokiniana exhibited increased growth and chlorophyll content at lower paraquat concentrations (0.01-1 mg l -1 ). However, higher concentrations (10 and 50 mg l -1 ) triggered oxidative stress characterized by elevated peroxidase (POD) activity and lipid peroxidation (malondialdehyde, MDA). Similarly, L. minor showed reduced chlorophyll content and biomass at higher paraquat doses, whereas its antioxidant activity increased at sublethal concentrations. Co-culturing of the 2 species intensified oxidative stress responses, particularly when paraquat was present, with both species exhibiting heightened hydrogen peroxide (H 2 O 2 ) levels and altered chlorophyll synthesis. Co-cultivation with C. sorokiniana enhanced the chlorophyll production by L. minor in the absence of paraquat, indicating potential synergistic interactions. These findings reveal that paraquat exposure disrupts the physiology of individual species and alters allelopathic interactions, with potential implications for ecosystem structure and function. Understanding these complex dynamics is essential for developing strategies to mitigate the ecological risks posed by herbicide contamination of aquatic environments.