Seed quality under elevated CO₂ differs in soybean cultivars with contrasting yield responses

Reduced grain and seed nutrient content in crops grown under elevated CO₂ concentrations (eCO₂) have raised concerns about future food security. Studies have reported that different seed elements responded differently to eCO₂. Additionally, the nutrient response to eCO₂ 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 eCO₂. We show that seed quality responded differently to eCO₂ for the two cultivars and that elements were differentially impacted. The strongest declines under eCO₂ were observed for Al, Ca, Fe, and Se while P and Mn were unaffected. Seed protein content increased under eCO₂ for the two cultivars. Oil content, however, showed a negative relationship with yield and declined under eCO₂. Using path analysis, we show that eCO₂ 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 eCO₂ 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 eCO₂ could adversely impact profits.