Unique root exudate tartaric acid enhanced cadmium mobilization and uptake in Cd-hyperaccumulator Sedum alfredii.

• About 2.30% of the assimilated 13C was incorporated into organic acid in rhizosphere of S. alfredii. • Tartaric acid is the unique root exudate from HE S. alfredii. • Tartaric acid was mainly distributed within the range of rhizosphere 0–6 mm. • Tartaric acid is highly efficient in Cd solubilization via the formation of soluble Cd-Tartrate complexes. • Tartaric acid enhanced Cd uptake in HE S. alfredii. Low molecular weight organic acids (LMWOA) involved in heavy metal tolerance, translocation, and accumulation in plants. However, underlying mechanism of LMWOA secretion in metal mobilization and uptake in hyperaccumulator still need to be identified. In this study, a 13C labeling rhizobox was designed to investigate the composition and distribution of LMWOA in the rhizosphere of S. alfredii. The result showed that about 2.30%, 2.25% and 2.35% of the assimilated 13C was incorporated into oxalic acid, malic acid, and tartaric acid in rhizosphere of S. alfredii after 13CO 2 assimilation, respectively. Oxalic acid, malic acid, and tartaric acid were the predominant LMWOA in rhizosphere soil solution of hyperaccumulating ecotype (HE) S. alfredii , however, almost no tartaric acid was detected for non-hyperaccumulating ecotype (NHE). Tartaric acid was identified as the unique root exudate from HE S. alfredii which was mainly distributed within the range of rhizosphere 0–6 mm. Tartaric acid significantly increased the solubility of four Cd minerals. HE S. alfredii treated with tartrate + CdCO 3 had higher Cd contents and larger biomass than CdCO 3 treatment. Cadmium accumulation in HE S. alfredii was promoted by the exudation of tartaric acid, which was highly efficient in Cd solubilization due to the formation of soluble Cd-tartrate complexes. [ABSTRACT FROM AUTHOR]