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

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 C-3 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 C-3 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 C-3 vascular plants will be similar regardless of the form of N assimilated.