不同土壤的还原状况对铁镉形态转化和水稻吸收的影响

采用土壤-蛭石联合培养,以填充蛭石的网袋模拟根际,置于红壤、水稻土、盐土中后淹水栽培水稻13 d.试验结果表明,水稻栽培期问,红壤、水稻土、盐土pH变化范围分别为6.05 ～6.78、6.47 ～7.33、6.42 ～7.44;有机质处理下,除红壤根际pH明显升高外,其余土壤根际和非根际pH均有所下降.各土壤对照根际Eh保持在233 ～ 385 mV;有机质处理使根际Eh下降,同时也导致除盐土外的非根际Eh上升.土壤还原溶解Fe与蛭石吸附Fe的90％以上均米自铁锰氧化物结合态铁(Oxide-Fe)组分,与溶液Eh、pe+ pH均有显著相关性,表明两表面同为Fe的氧化还原反应,但方向相反.水稻根表Fe膜的形成与根际氧化还原状况有关,在对照根际(高Eh)环境下,根表Fe含量随pH升高而降低,在有机质处理根际(低Eh)环境下则随pH升高而升高;在红壤中,根表Fe膜阻碍Fe的吸收,在水稻土和盐土中,根表Fe膜促进Fe吸收.根表Cd含量与根内Cd、地上部Cd有显著正相关;在红壤中,根表Fe膜阻碍了水稻Cd的吸附和吸收;水稻土和盐土中,根表Fe膜促进了水稻Cd的吸附和吸收.

Effects of soil redox condition on the transformations of Fe and Cd in soils and their uptake by rice

In a pot experiment rice seedlings were planted in mesh bags that were filled with vermiculite to simulate rhizosphere and the bags were imbedded separately in submerged red, paddy and saline soils for cultivation for 13days. Results show that during the rice cultivation period, pH in the red, paddy and saline soils varied in the range of 6.05~6.78, 6.47~7.33 and 6.47~7.44, respectively. In the OM (organic matter) treatments, all the soils, regardless of rhizospheric or nonrhizospheric, decreased in pH, except for rhizospheric red soil, which increased significantly. Eh in all the rhizospheric soils of the control treatments lingered within 233~385 mV, and treatment with OM reduced rhizospheric Eh, but increased nonrhizospheric Eh of the red and paddy soils. Oxide-Fe fraction accounted for more than 90% of the reductively dissolved Fe and vermiculite-absorbed Fe, which was significantly correlated with soil solution Eh and pe pH, indicating that Fe redox reactions occurred simultaneously on the surfaces of the soils and the vermiculites, but in opposite directions. The formation of iron plaque on root surface of the rice seedlings was related to redox conditions in rhizosphere. In the rhizospheres of CK (higher in Eh), Fe content on the root surface decreased with increasing pH, whereas in the rhizospheres of OM treatment (lower in Eh), Fe increased with increasing pH. In the red soil, iron plaques on the root surface retarded Fe absorption, while in the paddy and saline soils it acted reversely. Cd content on the root surface was significantly and positively related to Cd in root and in shoot. In the red soil iron plagued on the root surface retarded adsorption and uptake of Cd by rice, whereas in paddy and saline soils, it acted reversely too.