PHYSIOLOGICAL RESPONSES OF Eucalyptus camaldulensis (Dehnh.) TO SIMULATED GLYPHOSATE DRIFT

Abstract

Weed control with glyphosate produces damages in plantations of Eucalyptus camaldulensis, although the involved physiological mechanisms have not been completely elucidated. This work aimed at assessing the physiological responses of E. camaldulensis to simulated glyphosate drift. Greenhouse trials were performed with four-month-old E. camaldulensis clone117 seedlings. The herbicide drift was simulated applying doses of 0; 43,2; 86,4; 172,8 and 345,6 g a.e. ha⁻¹ glyphosate. Twenty-three days after the application, we measured gas exchange and chlorophyll a fluorescence. We also quantified Rubisco activity and indicator variables of oxidative stress. Glyphosate decreased carbon photosynthetic assimilation, increased non-photochemical quenching, induced stomatal closure, and increased photoinhibition. It also decreased Rubisco activity and increased photorespiration. The herbicide produced oxidative stress, and increased the activities in the enzymes catalase, ascorbate peroxidase, and superoxide dismutase, involved in the detoxification of reactive oxygen species. We concluded that glyphosate´s deleterious effects on the assimilation of CO₂ in E. camaldulensis are due to stomatal and non-stomatal effects. The decrease in Rubisco activity, the increase in photorespiration, and photoinhibition stand out among non-stomatal effects. The increase in the activity of the antioxidant system is insufficient to compensate for the production of H₂O₂ in photorespiration, which damages the photosynthetic apparatus.