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2.6.2 Photosynthesis

In generał, for all ninc species, after glyphosate exposure, ABS/RC, TRo/RC and DIo/RC parameters tend to increase, while ETo/RC and the F_V/F_M ratio tend to decrease (Figurę 2.1). However, therc was some specificity for each specie. For the green algae Ankistrodesmus falcatus the F_V/F_M ratio was higher at the highest glyphosate dose (Figurę 2.1 A). This is the only species showing an increase of F_V/F_M after glyphosate exposure. All other species had a F_v/F_m ratio significantly lower at the highest glyphosate concentration. Indeed, for Chlamydomonas reinhardtii (CPCCI25), Microcystis sp., Scenedesmus obliyuus (CPCC5), Microcystis ueruginosea (CPCC632) and Oocystis solitaria, the F_V/F_M ratio was lower at a glyphosate concentration of 500 pg I'¹ compared to lower concentrations. The ABS/RC parameter was increased for the majority of species at the glyphosate concentration of 500 pg F¹, except for Ankistrodesmus falcatus and Cryptomonas obovata (Figurę 2. IB). A similar increase was obscrved for the Dlo/RC parameter (Figurę 2.1C). Rcgarding TRo/RC, only a few species showed an increase at high glyphosate concentrations (500 and 1000 pg I*¹): Scenedesmus obliquus (CPCC5), Chlamydomonas reinhardtii (UTCCI25), Oocystis solitaria and Chlamydomonas snowi i, while the other species showed no difference from the control treatment (Figurę 2.ID). For ETq/RC, the majority of the species showed a decrease at the highest glyphosate concentration, cxcept for Ankistrodesmus falcatus and Cryptomonas obovata (Figurę 2.IE). There was a decrease of this parameter for the non-toxic cyanobacteria strain Microcystis ueruginosea (CPCC632), at a glyphosate concentration of 100 gg l’\

The effcctivc concentration inducing 10% of effect compared to the control treatment (EC|₀), shown in table 2.4, express the interspecific sensitivity of the different algal and cyanobacteria species, regarding growth and PS1I energy fluxcs. The growth ratę was the most sensitive parameter being affected by glyphosate exposure, exeept for Ankistrodesmus falcatus. For this specie, F_V/F_M, ABS\RC and TRo/RC were morę sensitive than the growth ratę, while DIo/RC and ETq/RC showed no sensitivity towards glyphosate. Cryptomonas obovata, the second least scnsitive species, showed no sensitivity of the photosynthetic parameters F_V/F_M, TRo/RC and ETo/RC. The other studied species were vcry sensitive to glyphosate regarding growth ratę (ECio< 10 pg I'¹), but their sensivivity toward the difTcrent

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