Elevated Atmospheric Carbon Dioxide and Weed Populations in Glyphosate Treated Soybean
2006
Ziska, Lewis H. | Goins, Ernie W.
Although rising atmospheric carbon dioxide (CO₂) is known to stimulate the growth of agronomic weeds, the impact of increasing CO₂ on herbicide efficacy has not been elucidated for field-grown crops. Genetically modified soybean [Glycine max (L.) Merr.] (i.e., Round-up Ready soybean) was grown over a 2-yr period at ambient and projected levels of atmospheric carbon dioxide (CO₂, 250 μmol mol⁻¹ above ambient), with and without application of the herbicide, glyphosate [N-(phosphonomethyl)glycine], to assess the impact of rising atmospheric carbon dioxide concentration [CO₂] on chemical efficacy of weed control. For both years, soybean showed a significant vegetative response to elevated [CO₂], but no consistent effect on seed yield. For 2003, weed populations for all treatments consisted entirely of C₄ grasses, with no [CO₂] effects on weed biomass (unsprayed plots) or glyphosate efficacy (sprayed plots). However, in 2004, weed populations were mixed and included C₃ and C₄ broadleaves as well as C₄ grasses. In this same year, a significant increase in both C₃ broadleaf populations and total weed biomass was observed as a function of [CO₂] (unsprayed plots). In addition, a [CO₂] by glyphosate interaction was observed with significant C₃ broadleaf weed biomass remaining after glyphosate application. Overall, these data emphasize the potential consequences for CO₂–induced changes in weed populations, biomass, and subsequent glyphosate efficacy in Round-up Ready soybean.
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