Changes in biomass and root: shoot ratio of field-grown Canada thistle (Cirsium arvense), a noxious, invasive weed, with elevated CO2: implications for control with glyphosate

Ziska, L. H., Faulkner, S., & Lydon, J. (2004). Changes in biomass and root: shoot ratio of field-grown Canada thistle (Cirsium arvense), a noxious, invasive weed, with elevated CO2: implications for control with glyphosate. Weed Science, 52(4), 584-588. PDF.

Summary

Rising atmospheric CO2 acts as both a powerful greenhouse gas and a resource for plant photosynthesis. The addition of this CO2 ‘fertilizer’ can lead to increased plant growth. But, for invasive plants, increased growth could also change the efficacy of standard chemical treatments.  Ziska et al. (2004) assessed the efficacy of glyphosate treatment on Canada thistle (Cirsium arvense) grown under ambient and elevated CO2 conditions. With increased CO2, Canada thistle shoot growth increased by ~30%, whereas root growth increased by ~300%. This large increase in investment in root biomass with elevated CO2 translated into significantly reduced efficacy of glyphosate treatment.  Plants grown in elevated CO2 were able to recover after the chemical application such that there was no difference in aboveground biomass between the sprayed treatment and unsprayed control. In contrast, aboveground biomass of the sprayed plants under ambient CO2 was significantly lower (25% of the biomass) of the unsprayed control. These results suggest that plants grown under elevated CO2 could increase their root biomass allocation, making chemical treatment less effective. 

Take home points

  • Canada thistle grown under elevated (~650 ppm) CO2 increased its root:shoot biomass allocation

  • Increased root biomass makes chemical treatment of shoots less effective, because plants are able to regrow

Management implications

  • Chemical treatments might become less effective with increased CO2

  • Weed pulling or other treatments that specifically target roots might become increasingly successful

Keywords

Impact Study; Herbicides; Experiment; Invasive Plant; Terrestrial Habitat; Cirsium arvense; Canada Thistle