Increased temperatures may safeguard the nutritional quality of crops under future elevated CO₂ concentrations

Iron (Fe) and zinc (Zn) deficiencies are a global human health problem that may worsen by the growth of crops at elevated atmospheric CO₂ concentration (eCO₂ ). However, climate change will also involve higher temperature, but it is unclear how the combined effect of eCO₂ and higher temperature will affect the nutritional quality of food crops. To begin to address this question, we grew soybean (Glycine max) in a Temperature by Free-Air CO₂ Enrichment (T-FACE) experiment in 2014 and 2015 under ambient (400 μmol mol^-1 ) and elevated (600 μmol mol^-1 ) CO₂ concentrations, and under ambient and elevated temperatures (+2.7°C day and +3.4°C at night). In our study, eCO₂ significantly decreased Fe concentration in soybean seeds in both seasons (-8.7 and -7.7%) and Zn concentration in one season (-8.9%), while higher temperature (at ambient CO₂ concentration) had the opposite effect. The combination of eCO₂ with elevated temperature generally restored seed Fe and Zn concentrations to levels obtained under ambient CO₂ and temperature conditions, suggesting that the potential threat to human nutrition by increasing CO₂ concentration may not be realized. In general, seed Fe concentration was negatively correlated with yield, suggesting inherent limitations to increasing seed Fe. In addition, we confirm our previous report that the concentration of seed storage products and several minerals varies with node position at which the seeds developed. Overall, these results demonstrate the complexity of predicting climate change effects on food and nutritional security when various environmental parameters change in an interactive manner.