THE UNPRECEDENTED RISE IN ATMOSPHERIC CO2 CONCENTRATION ([CO2]) IS EXPECTED TO INCREASE THE YIELDS OF C3 CROPS BUT AT THE COST OF IMPORTANT MINERAL NUTRIENTS. DESPITE THE LARGE BODY OF LITERATURE DOCUMENTING THE EXPERIMENTAL EFFECTS OF ELEVATED [CO2] ON BIOMASS AND NUTRIENT ACCUMULATION, THE PHYSIOLOGICAL MECHANISMS THAT LINK THE INCREASED BIOMASS RESPONSE WITH ALTERATIONS IN MINERAL NUTRITIONAL CONTENT HAVE NOT BEEN EMPIRICALLY TESTED. IN SOYBEAN (GLYCINE MAX L. MERR.), THERE IS SIGNIFICANT PHENOTYPIC VARIATION FOR BIOMASS AND MINERAL CONTENT RESPONSES TO ELEVATED [CO2] THAT CAN BE USED TO DISSECT THE UNDERLYING MECHANISMS OF TRAIT RESPONSES TO RISING [CO2]. EIGHT CULTIVARS OF SOYBEAN WILL BE UTILIZED IN THIS PROPOSAL TO ANSWER THREE RESEARCH AIMS: (1) EMPIRICALLY TEST THE HYPOTHESIZED PHYSIOLOGICAL AND MOLECULAR MECHANISMS OF MINERAL COMPOSITION RESPONSE TO ELEVATED [CO2]; (2) BUILD MATHEMATICAL MODELS OF THE UNDERLYING PHYSIOLOGY OF ELEMENTAL ACCUMULATION TO TEST HOW ELEVATED [CO2]ALTERS ELEMENTAL ACCUMULATION IN PLANTS; AND (3) VALIDATE OUTPUTS OF THESE MODELS IN A FIELD SETTING TO DETERMINE THE MOST LIKELY MECHANISM(S) ASSOCIATED WITH LOWER MINERAL NUTRIENTS IN PLANTS IN ELEVATED [CO2]. OUTPUTS FROM GROWTH CHAMBER AND FIELD EXPERIMENTS WILL BE USED AS INPUTS TO BUILD MODELS OF THE UNDERLYING PHYSIOLOGY OF ELEMENTAL ACCUMULATION UNDER ELEVATED [CO2]. OUTCOMES FROM THIS PROPOSAL CAN BE TRANSLATED DIRECTLY INTO MOLECULAR RESOURCES TO DEVELOP MORE CLIMATE-RESILIENT CROPS.