• Free Air CO2 Enrichment;
  • demography;
  • growth analysis;
  • C3 and C4 photosynthesis;
  • Amaranthus rudis;
  • Chenopodium album;
  • Glycine max

Davis AS & Ainsworth EA (2012). Weed interference with field-grown soyabean decreases under elevated [CO2] in a FACE experiment. Weed Research52, 277–285.


Rising atmospheric [CO2] is predicted to affect C3 and C4 weed interference with crop species differently, with C3 weeds benefiting more from elevated [CO2] (eCO2) than C4 species. Our aim was to quantify impacts of eCO2 on C3 and C4 weeds at three levels of biological organisation: individual, population and community. We conducted a field study in 2007 and 2008 within the SoyFACE experiment in Champaign, Illinois, USA, in which Amaranthus rudis (C4) and Chenopodium album (C3) were grown with soyabean. This is a Free Air CO2 Enrichment (FACE) experiment. Elevated [CO2] influenced weeds at all levels of biological organisation. However, community-level impacts were largest. Interference by A. rudis and C. album with soyabean was 37% and 11% lower, respectively, in eCO2. In residual weed communities under ambient [CO2] (aCO2), C3 and C4 species were equally likely to dominate the community, whereas in eCO2, there was a 90% chance of community dominance by C3 species. Future investigations of weed ecology and global change under FACE conditions may improve their inference space by including sources of environmental stress such as ozone, heat and drought.