Glyphosate-based herbicide (GBH) applications were reported to induce physiological damages to glyphosate-resistant (GR) soybean, which were mainly attributed to aminomethylphosphonic acid (AMPA). In order to study glyphosate and AMPA dynamics in plants and associated phytotoxic effects, a greenhouse experiment was set where GR soybeans were exposed to GBH (0.7 to 4.5 kg glyphosate ha-1) and sampled over time (2, 7, 14, and 28 days after treatment (DAT)). Hydrogen peroxide content increased 2 DAT, while a decrease was observed for the effective quantum yield (2, 7, 14 DAT), stomatal conductance (2 DAT), and biomass (14 DAT). Glyphosate content was higher in leaves, followed by stems, and then roots. AMPA content tended to increase with time, especially in roots, and the amount of AMPA in roots was negatively correlated to mostly all phytotoxicity indicators. This finding is important since AMPA residues are measured in agricultural soils several months after GBH applications, which could impact productivity in GR crops.
Keywords: HO; biomass; effective quantum yield; glyphosate and AMPA toxicokinetics; glyphosate-based herbicides; glyphosate-resistant soybean; stomatal conductance.