Differential responses of diatom and dinophyte microalgae to the presence of glyphosate herbicide in the medium

Abstract

A comprehensive experimental study of the effect of glyphosate herbicide on morphological, structural-functional, cytometric and fluorescent parameters of microalgae (dinoflagellate Prorocentrum cordatum, Prorocentrum micans and marine diatom microalgae Thalassiosira weissflogii, Cyclotella caspia) was carried out. Glyphosate inhibits the growth of diatom algae, reducing the yield of final biomass. The cytotoxic effect of glyphosate is manifested by an increase in the production of reactive oxygen species, depolarisation of mitochondrial membranes, imbalance in the enzymatic (esterase) activity of cells, and a decrease in the efficiency of the photosynthetic apparatus of cells. A number of other specific reactions are also observed: an increase in algal cell complexity, a decrease in chlorophyll autofluorescence and the percentage of living cells. The opposite effect was found with dinophyte algae. Glyphosate stimulated the growth of dinoflagellates. Hormesis growth of the potentially toxic dinophyte alga Prorocentrum cordatum was attributed to the ability of this species to grow at the expense of glyphosate as the sole source of phosphorus. At the same time, the algae showed an increase in the efficiency of the photosynthetic apparatus of cells and their enzymatic (esterase) activity. The reason for hormesis growth of Prorocentrum micans at glyphosate concentration of 100 µg L−1 is probably due to intensive bacterial growth in cultures, which promoted rapid mineralisation of glyphosate and increased phosphorus bioavailability for microalgae. The herbicide at concentrations of 150 and 200 µg L−1 had a cytotoxic effect on P. micans. Thus, the species specificity of microalgae to the impact of glyphosate in natural conditions is potentially dangerous by changing the species structure of biocenoses, in particular, by decreasing the number of diatom algae and increasing the contribution of potentially toxic species of dinophyte algae.