PHOTOSYNTHETIC PARAMETERS IN GLYPHOSATE-TREATED SUGAR-BEET (BETA-VULGARIS L)

Variable fluorescence and carbon dioxide exchange rate (CER) were meas ured in intact leaves of glyphosate-treated sugarbeet plants, to inves tigate rapid effects on photosynthesis. In one experiment, a significa nt effect on variable fluorescence and CER was found within 8 h after herbicide application. The effect on stomatal conductance was not sign ificant. In a second experiment, the effects of light or dark conditio ns during herbicide application and 24 h later were evaluated. Under l ight conditions glyphosate significantly reduced variable fluorescence after 4 h. However under initial conditions of 24 h darkness, followe d by alternating 8 h light/8 h dark, the effect was not significant un til 44 h after treatment, by which time the plants had received severa l hours of light. The effect on variable fluorescence 8 h after herbic ide application correlated positively with plant survival 7 days later .