Abstract: Accumulation, chemical form and molecular distribution of Cd in two water spinach varieties, viz. Taiwan308 and Qiangkunqinggu were studied with a hydroponic experiment. The results showed that Cd concentrations in leaves, stems and roots of Taiwan308 were 3.17, 3.55, 39.1 mg·kg^-1， respectively, which were significantly higher than those of 2.06, 2.35, 33.5 mg·kg^-1 correspondingly for Qiangkunqinggu at the treatment of Cd 1.0 mg·L^-1. Cd concentrations in leaves and stems of Taiwan308 were 3.75 and 4.15 mg·kg^-1 respectively, which were significantly higher than those of 2.68 and 3.43 mg·kg^-1 correspondingly in Qiangkunqinggu at the treatment of 5.0 mg·L^-1 Cd, while Cd concentration in roots of Taiwan308 was 55.8 mg·kg^-1, and obviously less than that of 83.7 mg·kg^-1 in Qiangkunqinggu. The results of Cd chemical forms showed that ethanolextractable Cd was dominant in the leaves, while in the stems and roots, the main forms were ethanolextractable and NaClextractable Cd in the two water spinach varieties. Compared with Qiangkunqinggu in leaves, stems and roots, Taiwan308 had a higher proportion of more mobile H₂Oextractable Cd, but a lower proportion of less dissoluble HAcextractable and HClextractable Cd. The levels of Cd concentration and the varieties of water spinach had obvious effects on Cd chemical forms in vivo, especially in roots. The results of Cd molecular distribution showed that the majority of soluble Cd in leaves was bounded to low and high molecular weight components, while in roots Cd was bounded to phytochelatins (PCs) and some proteins of 10-20 kDa. The concentration of CdPCs in roots of Qiangkunqinggu was lower than that of Taiwan308, which would decrease the Cd translocation from root to aboveground part, finally leading to the lower concentration of the edible parts.

Key words: dominant species, niche breadth, generalized additive model, forest community, niche overlap