Fig. 1. Quantification of above ground weed biomass in three general categories, (C3 broadleaf, C4 broadleaf and C4 grass) when grown at ambient and elevated (+250 µmol mol–1) [CO2] in Round-up Ready soybean without glyphosate application in 2004. Variation for a given weed category was tested by a one-way ANOVA, with three replicates. *, P < 0.05; **, P < 0.01; ***, P < 0.001.