Current ‘gold standard’ research shows that elevated CO2 levels (such as we are likely to experience in our lifetimes) drive down the concentrations of important minerals like calcium, potassium, zinc and iron by 8 percent, on average, and drive down the protein contents of wheat and rice by 6 percent and 8 percent, respectively.
http://www.politico.com/agenda/story/2017/09/13/food-nutrients-carbon-dioxide-000511