For more details, I recommend this Nature article: https://www.nature.com/scitable/knowledge/library/effects-of-rising-atmospheric-concentrations-of-carbon-1325

For more details, I recommend this Nature article: https://www.nature.com/scitable/knowledge/library/effects-of-rising-atmospheric-concentrations-of-carbon-13254108 https://www.nature.com/scitable/knowledge/library/effects-of... The short version, if I remember it correctly: Plants open and close their pores ("stomata") to balance the need to get CO_2 from the air with the need to conserve water, which easily evaporates away and then needs to be replenished through the roots. If we give plants lots of CO_2, they will close their pores to prevent water loss (because who knows when it'll next rain, right?). But the micronutrients, including the N required to make proteins, come from the ground – so the plants' own mechanism to minimize having to rely on water from the ground results in the plant accumulating fewer micronutrients.