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.