Rising atmospheric CO concentration inhibits nitrate assimilation in shoots but enhances it in roots of C plants.

We have proposed that rising atmospheric CO concentrations inhibit malate production in chloroplasts and thus impede assimilation of nitrate into protein in shoots of C plants, a phenomenon that will strongly influence primary productivity and food security under the environmental conditions anticipated during the next few decades. Although hundreds of studies support this proposal, several publications in 2018 and 2019 purport to present counterevidence. The following study evaluates these publications as well as presents new data that elevated CO enhances root nitrate assimilation in wheat and Arabidopsis while it inhibits shoot nitrate assimilation.