Cadmium found in peanut (Arachis hypogaea L.) kernels mainly originates from root uptake rather than shell absorption from soil

Roots and shells are two potential organs through which peanut plants absorb cadium (Cd) from soils; however, the relative contributions of the two uptake pathways (root uptake and shell absorption) to kernel Cd accumulation and their translocation characteristics are poorly understood. In this study, the relative contributions of the two pathways to Cd accumulation in two peanut cultivars, Xianghua2008 (XH) and Yueyou43 (YY), were accurately assessed by labeling rooting and podding zone soils with ¹¹³Cd and ¹¹¹Cd isotopes (0.3 mg kg^-1 dry soil), respectively, in a split-pot design. The results showed that approximately 96% of the Cd accumulated in the peanut kernels was derived from root uptake, while only 4% originated from shell absorption. Only 1% of the Cd accumulated in whole peanut plants was attributed to shell absorption, of which 41%–44% was retained in shells and 56%–59% was translocated to kernels. In contrast, the Cd absorbed by roots was efficiently translocated into all plant organs, of which 80%–84% was distributed in shoots. Although YY accumulated 1.3 times more Cd in whole plants than XH, the relative contributions of the two pathways to Cd accumulation in each plant organ were barely affected by peanut cultivars. Due to the strong retention effect of shells, shell-derived Cd was approximately 2 times higher than root-derived Cd in shells. These results would improve the understanding of Cd accumulation processes in peanut plants, revealing that the root uptake pathway contributes predominantly to the Cd concentration in peanut kernels, based on which strategies and technology for the reduction of Cd in peanut plants could be designed and developed.