Nutrient Challenges in a Changing Atmosphere: Investigating Biomass Growth and Mineral Concentration Changes in Soybean Plants under Elevated CO2

Rising atmospheric CO2 levels, projected to reach [~]650 ppm by 2050, threaten the nutritional value of food crops. This rise is expected to increase biomass yield in C3 plants through enhanced photosynthesis and water-use efficiency. However, elevated CO2 (eCO2) reduces protein, nitrogen, and essential minerals like zinc (Zn) and iron (Fe) in plant leaves and seeds, posing a global nutrition risk. We conducted an experiment using Open Top Chambers to examine the response of three soybean cultivars (Clark, Flyer, and Loda) to ambient ([~]410 ppm) and eCO2 ([~]610 ppm) conditions. These cultivars were selected due to their contrasting responses to eCO2. Measurements of physiological parameters (i.e., biomass, and nutrient concentration) were taken at different growth stages. Our results showed that eCO2 increased carbon assimilation, leading to higher aboveground biomass and seed yield (through increased seed number) while root biomass remained unchanged. eCO2 also reduced stomatal conductance and transpiration. There was a significant decrease in seed nutrient concentration at maturity, particularly iron (Fe), phosphorous (P), potassium (K), and magnesium (Mg), in plants grown in eCO2. These findings suggest that increased yield, reduced transpiration, and unchanged root biomass are key drivers of nutrient dilution in seeds under eCO2.