Phytotoxicity of the Roundup® Max herbicide on the non-target species Lemna gibba in field and laboratory studies

Abstract

The use of the herbicide formulate Roundup® in transgenic crops of the Pampa´s plains of Argentina has extensively increased, though there is scarce information on its impact on non-target vascular plants from agro-ecosystem related surface waters. Within this frame, the sensitivity of the macrophyte Lemna gibba L. to Roundup® Max was studied in standardized laboratory conditions and field experiments. In the laboratory, phytotoxic effects were assessed on the growth rate (GR) and total chlorophyll content (TCC). The GR was affected at 1 mg/L and TCC at 7.5 mg/L as active ingredient. Effects varied along testing time: toxicity was higher at low concentrations at the beginning, but diminishing during exposure, while at higher concentrations toxicity increments during testing. Also, a reduction of frond and root growth was detected. Field experiments with caged plants placed close to field crops showed an inhibition of 35.5 % in biomass production (dry weight) and 75.5 % in TCC when a dose of 1 kg/ha was applied. Although, in a second dose, only an inhibition effect on TCC of 53.9 % was detected. The assessment of the herbicide drift did not show an influence of this exposure route on the plants for the studied scenery. The lowest glyphosate concentration producing an effect in the laboratory is in agreement with the detected levels of the herbicide in the water body associated with effects in field experiments.