Elevated CO₂ effects on nitrogen assimilation and growth of C₃ vascular plants are similar regardless of N-form assimilated

Abstract

Atmospheric carbon dioxide concentration ([CO₂]) increased from around 280 ppm in 1750 to 400 ppm in 2016 and is likely to continue to increase throughout this century. It has been argued that wheat, Arabidopsis, and C₃ plants in general respond more positively to elevated atmospheric [CO₂] under ammonium (NH₄⁺) nutrition than under nitrate (NO₃⁻) nutrition because elevated CO₂ inhibits their photoreduction of NO₃⁻ and hence reduces their total plant nitrogen (N) assimilation and ultimately growth. Here, it is argued that the weight of evidence in the literature indicates that elevated atmospheric [CO₂] does not inhibit NO₃⁻ assimilation and growth of C₃ vascular plants. New data for common bean and wheat support this view and indicate that the effects of elevated atmospheric [CO₂] on N assimilation and growth of C₃ vascular plants will be similar regardless of the form of N assimilated.