Will rising atmospheric CO₂ concentration inhibit nitrate assimilation in shoots but enhance it in roots of C₃ plants?

Abstract

Bloom et al. proposed that rising atmospheric CO₂ concentrations ‘inhibit malate production in chloroplasts and thus impede assimilation of nitrate into protein of C₃ 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 C₃ 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 C₃ 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 C₃plants. Measurement of the partitioning of NO₃¯ assimilation between root and shoot of C₃ 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 .