Can glyphosate stimulate photosynthesis?

Gas-exchange and biomass growth was measured on barley plants sprayed with glyphosate in order to investigate what might cause the growth increase observed in low dose glyphosate treated plants. Gas-exchange over 7 days after spraying was measured together with photosynthesis/irradiance and photosynthesis/CO2 curves. In addition, growth experiments at 100, 200, 400 and 800 ppm CO2 were conducted. Dark respiration rates increased in response to the glyphosate treatment, but so did photosynthesis at doses of 11–45 g a.e. ha−1. The increase in photosynthetic rates was mainly due to an increased efficiency of CO2 fixation under irradiance and CO2 saturated conditions. The photosynthesis measurements were confirmed by the growth experiments, where glyphosate growth stimulations were observed only at 400 and 800 ppm CO2. It can, hence, be concluded that low glyphosate doses can stimulate photosynthesis, though the causes behind this increase is still not understood.