Abstract
Reduced grain and seed nutrient content in crops grown under elevated CO 2 concentrations (eCO 2 ) have raised concerns about future food security. Studies have reported that different seed elements responded differently to eCO 2 . Additionally, the nutrient response to eCO 2 varied across species and cultivars. This study investigated the response of seed quality in two soybean cultivars (HS93‐4118 and Loda) previously shown to have different yield responses to eCO 2 . We show that seed quality responded differently to eCO 2 for the two cultivars and that elements were differentially impacted. The strongest declines under eCO 2 were observed for Al, Ca, Fe, and Se while P and Mn were unaffected. Seed protein content increased under eCO 2 for the two cultivars. Oil content, however, showed a negative relationship with yield and declined under eCO 2 . Using path analysis, we show that eCO 2 reduced the seed content for some elements through increasing seed yield, effectively diluting the elemental concentrations, while other elements were reduced in a yield‐independent manner. Despite the decline in the seed concentration for some elements, the overall yield per hectare of elements, protein, and oil under eCO 2 increased because of greater seed yield. We quantified the economic impact of altered seed composition and show that the decline in oil content with increasing soybean yield at eCO 2 could adversely impact profits.