Effect of glyphosate-based herbicides on the photosynthetic responses of the macrophyte Egeria densa Planch. from topical lotic ecosystems

Abstract

The effects of pesticide pollution on eco-physiological responses in primary producers are understudied. To partly over-come this gap, this study evaluated the effects of a glyphosate-based herbicide, Roundup® (three nominal concentrations: 0.28 mg/L [Treatment T0.28]; 3.5 mg/L [T3.5]; and 6 mg/L [T6]), and its main degradation product, aminomethylphosphonic acid (AMPA) (0.03 mg/L [T0.03]), on the photosynthetic responses of an aquatic macrophyte species, Egeria densa Planch. The net photosynthetic rate (NPR) and dark respiration rate (DRR) were evaluated by the dissolved oxygen evolution method, while some PSII performance parameters were measured by a Chl-a fluorescence-based method. Additionally, the chlorophyll a content was measured. The experimental data showed that E. densa had significant losses in photosynthetic efficiency under Roundup® and AMPA exposure, with reductions in the NPR (reduction of-61 % for T3.5; –90 % for T6; and –161 % for T0.03, compared to control) and chlorophyll a content (–82 % for T0.28, –79 % for T3.5, –82 % for T6, and –28 % for T0.03) and increases in the DRR (+150 % for T3.5, +130 % for T6, and +271 % for T0.03). The results from the Chl-a fluorescence measurements registered statistically significant differences between the Roundup® treatments and the control group for the effective quantum yield (+56 % for T0.28, +43 % for T3.5, and +56 % for T6) and for non-photochemical extinction (+67% for T0.28, +73 % for T3.5, and +59 % for T6). Taken together, the findings of the experiments with E. densa indicate that the negative effects from the glyphosate-based herbicide Roundup® on primary producers might be common and widespread in tropical and subtropical aquatic environments in Brazil.