Effect of atrazine on growth, photosynthesis, and between-strain variability in Scenedesmus subspicatus (Chlorophyceae)

The magnitude of between-strain differences in the sensitivity of algal spe cies to toxicants is not well known. Yet, informations obtained with a sing le strain are used for ecotoxicological assessment and for interspecific co mparisons. Using 12 strains, we determined whether intraspecific variabilit y occurs in the green alga Scenedesmus subspicatus. We examined growth, pho tosynthetic activity, and short-term sensitivity thereof to the herbicide a trazine (500 mu g . L-1) as well as how these responses are affected by chr onic exposure to low atrazine concentrations (0, 1, 5, and 20 mu g . L-1). Independent of chronic exposure to atrazine, the strains differed in growth rate and photosynthesis rate. Yet the short-term sensitivity to atrazine w as affected by the chronic treatments. All but one strain became more toler ant, their short-term sensitivity being inversely related to the applied at razine concentration and dependent on the duration of exposure. Differences in response to increments in atrazine concentration resulted in difference s in rank order of sensitivity of strains. Moreover, between-strain variabi lity was markedly higher in the atrazine treatments than in the controls. T hese results can be explained by the significant role of genotype versus en vironment interactions in determining intraspecific differences in adaptive physiological responses of S. subspicatus to chronic exposure to atrazine.