Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance spectroscopy (

1

H NMR and

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C NMR) were used to investigate the structural characteristics of dissolved organic matter (DOM) in the rhizosphere soil of a low-Cd cultivar (QLQ) and a high-Cd cultivar (T308) of water spinach (Ipomoea aquatica Forsk.). The results showed that carbohydrates were the main components of DOM in the rhizosphere soil of the two cultivars

and the contents of alkyl and aromatic substances were relatively low. There were obvious differences in the structural characteristics of DOM between the two cultivars. The relative contents of carboxylic C and longchain aliphatic C of DOM in the rhizosphere soil of QLQ were lower than those of T308

but that of aromatic substance of QLQ was higher. Alkyl substance of DOM in the rhizosphere soil of QLQ possessed the characteristics of relatively high content，short branched chain and high branched chain. Although carbohydrate H content of DOM in the rhizosphere soil of QLQ was lower than that of T308

carbohydrate C content was higher than that of T308

which suggested that there might be differences in the structure of carbohydrates of DOM in the rhizosphere soil between the cultivars. The results indicated that the structural characteristics of DOM in the rhizosphere soil of the low-Cd cultivar might influence Cd behavior and bioavailability

leading to relatively low ability to activate soil Cd

which would be associated with its low Cd accumulation.