Impact of Elevated CO(2) on Seed Quality of Soybean at the Fresh Edible and Mature Stages

Although the effect of elevated CO(2) (eCO(2)) on soybean yield has been well documented, few studies have addressed seed quality, particularly at the fresh edible (R6) and mature stages (R8). Under the current global scenario of increasing CO(2) levels, this potentially threatens the nutritional content and quality of food crops. Using four soybean cultivars, we assessed the effects of eCO(2) on the concentrations of crude protein, crude oil, and isoflavones and analyzed the changes in free amino acids, fatty acids, and mineral elements in seeds. At R6, eCO(2) had no influence on soybean seed protein and oil concentrations. At R8, eCO(2) significantly decreased seed protein concentration but increased seed oil concentration; it also significantly decreased total free amino acid concentration. However, at the same stage, the proportion of oleic acid (18:1) among fatty acids increased in response to eCO(2) in the cultivars of Zhongke-maodou 2 (ZK-2) and Zhongke-maodou 3 (ZK-3), and a similar trend was found for linoleic acid (18:2) in Zhongke-maodou 1 (ZK-1) and Hei-maodou (HD). Total isoflavone concentrations increased significantly at both the R6 and R8 stages in response to eCO(2). Compared with ambient CO(2), the concentrations of K, Ca, Mg, P, and S increased significantly under eCO(2) at R6, while the Fe concentration decreased significantly. The response of Zn and Mn concentrations to eCO(2) varied among cultivars. At R8 and under eCO(2), Mg, S, and Ca concentrations increased significantly, while Zn and Fe concentrations decreased significantly. These findings suggest that eCO(2) is likely to benefit from the accumulation of seed fat and isoflavone but not from that of protein. In this study, the response of seed mineral nutrients to eCO(2) varied between cultivars.