Will rising atmospheric CO 2 concentration inhibit nitrate assimilation in shoots but enhance it in roots of C 3 plants?

Bloom et al. proposed that rising atmospheric CO2 concentrations 'inhibit malate production in chloroplasts and thus impede assimilation of nitrate into protein of C-3 plants, a phenomenon that will strongly influence primary productivity and food security under the environmental conditions anticipated during the next few decades'. Previously we argued that the weight of evidence in the literature indicated that elevated atmospheric [CO2] does not inhibit NO3- assimilation in C-3 plants. New data for common bean (Phaseolus vulgaris) and wheat (Triticum aestivum) were presented that supported this view and indicated that the effects of elevated atmospheric [CO2] on nitrogen (N) assimilation and growth of C-3 vascular plants were similar regardless of the form of N assimilated. Bloom et al. strongly criticised the arguments presented in Andrews et al. Here we respond to these criticisms and again conclude that the available data indicate that elevated atmospheric [CO2] does not inhibit NO3- assimilation of C-3 plants. Measurement of the partitioning of NO3- assimilation between root and shoot of C-3 species under different NO3- supply, at ambient and elevated CO2 would determine if their NO3- assimilation is inhibited in shoots but enhanced in roots at elevated atmospheric CO2.