Effects of Glyphosate on the Planktonic Microbiota: An Experimental Approach

Glyphosate is one of the most widely used herbicides in the world, including in Brazil, and its dispersion through habitats and surface waters can impact entire aquatic ecosystems. However, experimental studies evaluating the effects of pesticides on whole planktonic communities, considering attributes such as richness, density and composition-remain scarce. This study evaluated the effects of different glyphosate concentrations on freshwater planktonic microbiota, encompassing cyanobacteria, algae, testate amoebae, autotrophic and heterotrophic nanoflagellates, ciliates, rotifers and copepods. We experimentally simulated four contamination scenarios in freshwater microcosms: (i) control (no glyphosate), (ii) low glyphosate (30 μg/L^-1), (iii) high glyphosate (500 μg/L^-1), (iv) the maximum allowed in Brazil (65 μg/L^-1). The effects of glyphosate varied among biological groups, underscoring the complexity of community-level responses to contamination. Some groups, such as autotrophic and heterotrophic nanoflagellates, testate amoebae, rotifers, and copepods, responded only in density, with the total microfaunal community following a similar trend. Shifts in species composition were observed for testate amoebae (species replacement) and cyanobacteria (changes in richness), both of which contributed most to beta diversity variation under pesticide exposure. Microcosms exposed to higher glyphosate concentrations exhibited more distinct community compositions compared to the control, suggesting a shift toward more resistant species. These findings highlight the importance of protecting aquatic environments from pesticide contamination, as both individual species and entire communities exhibit differential sensitivity to chemical stressors, potentially affecting ecosystem functioning and services.