[Changes of Cd forms on wheat root-soil interface under stress of combined Cd and chlorimuron-ethyl]

With rhizobox experiment, this paper studied the changes of Cd forms on wheat root-soil interface under the stress of combined cadmium (Cd) and chlorimuron-ethyl. The root-soil interface (0-5 mm) was separated into 6 parts every other 1 mm, and the sampling time was 14, 21, 28, 35 and 42 days after treatment. The correlativity between Cd forms and Cd absorption by wheat was made to assess the availability of each Cd form. The results showed that exchangeable Cd showed different spatial effect during various growth periods. The trend of carbonate-bound Cd and Fe-Mn oxide-bound Cd transforming to exchangeable Cd was weaken, but the trend of the two Cd forms transforming to residual Cd was strengthened from root-center zone to non-rhizosphere. The concentration of organic-bound Cd varied significantly in neighboring root zone. During the whole experiment period, the concentrations of carbonate-bound Cd, Fe-Mn oxide-bound Cd and organic-bound Cd decreased, while that of residual Cd increased. Correlation analysis suggested that exchangeable Cd and organic-bound Cd nearby the root were the main Cd forms that could be absorbed by wheat. It could be concluded that the transformation of carbonate-bound Cd and Fe-Mn oxide-bound Cd and the concentration of exchangeable Cd were affected by chlorimuron-ethyl significantly.