Sublethal effects of environmentally relevant run‐off concentrations of glyphosate in the root zone of Ludwigia peploides (creeping water primrose) and Polygonum hydropiperoides (smartweed)

As one of the most widely applied agricultural chemicals in the world, glyphosate has many effects on the environment. The present study quantified plant responses to exposure by glyphosate through the root zone for a range of concentrations (0, 10, 100 and 1000 μg L⁻¹). Ludwigia peploides and Polygonum hydropiperoides were grown in a greenhouse and given a single exposure to glyphosate via the root zone. The growth and physiological parameters were measured before exposure and for 18 days postexposure. The growth variables that were measured included the relative growth rate, stem length increase, biomass and root‐to‐shoot‐ratios. The physiological variables that were measured were the chlorophyll content index and chlorophyll fluorescence. The data analyses revealed that the root‐zone glyphosate affected some of the measured variables in P. hydropiperoides more than for L. peploides. Polygonum hydropiperoides showed a significant decrease in the root‐to‐shoot ratios for the 100 μg L⁻¹treatment, compared to the 10 μg L⁻¹treatment. The chlorophyll content index of the treated plants was significantly reduced in P. hydropiperoides, compared to the untreated plants on Days 7 and 18. Ludwigia peploides was affected only on the day after exposure, with the chlorophyll fluorescence parameters being significantly less for the 1000 μg L⁻¹treatment, compared to the 10 μg L⁻¹treatment. Glyphosate‐treated P. hydropiperoides showed a decreased chlorophyll content and reduced chlorophyll fluorescence parameters. In contrast, L. peploides showed a decrease in the chlorophyll fluorescence parameters but no reduction in its chlorophyll content. In addition to demonstrating the adverse effects of root exposure to glyphosate for the study species, these data help to partially explain the highly invasive and persistent nature of L. peploides in marginal aquatic environments, such as agricultural ditches.