Exotic C₄Grasses Have Increased Tolerance to Glyphosate under Elevated Carbon Dioxide

Abstract

The increase in atmospheric CO 2 levels can influence the growth of many invasive exotic plant species. However, it is not well-documented, especially for C 4 plants, how these growth responses will alter the effectiveness of the world's most widely used herbicide for weed control, glyphosate. We aimed to address this question by carrying out a series of glasshouse experiments to determine if tolerance to glyphosate is increased in four C 4 invasive exotic grasses grown under elevated CO 2 in nonlimiting water conditions. In addition, traits including specific leaf area, leaf weight ratio, leaf area ratio, root : shoot ratio, total leaf area, and total biomass were measured in order to assess their contribution to glyphosate response under ambient and elevated CO 2 levels. Three of the four mature grass species that were treated with the recommended concentration of glyphosate displayed increased tolerance to glyphosate under elevated CO 2 . This was due to increased biomass production resulting in a dilution effect on the glyphosate within the plant. From this study, we can conclude that as atmospheric CO 2 levels increase, application rates of glyphosate might need to be increased to counteract the growth stimulation of invasive exotic plants.