外源Cd对小白菜吸收与分配Cd、Zn的影响

Uptake and Distribution of Cd and Zn by Pak Choi in Different Growth Stages in Two Paddy Soils Under Cd Treatment

采用盆栽试验研究外加Cd处理下红沙泥田和乌栅土中小白菜（Brassica chinensisL.）[四月慢（SYM）和高梗白（GGB）]对Cd、Zn的吸收与分配规律。结果表明：（1）小白菜对Cd、Zn的吸收积累受土壤类型、蔬菜品种和外源Cd剂量的影响,四月慢吸收Cd能力比高梗白强,外加Cd处理、土壤、品种间的正交互作用使小白菜植株Cd/Zn比值提高;（2）小白菜食用部位Cd/Zn比值并不服从于植株对Cd、Zn的总吸收量之比,而是取决于其在根和地上食用部位中的分配,Cd的地上部分配系数为56.3%-71.1%,而Zn则为77.6%-80.6%。在一定Cd处理水平下,地上部Cd分配系数下降,而Zn分配系数无明显变化,从而减缓了Cd/Zn比值升高的趋势,使小白菜地上部受Cd毒害的风险性降低;（3）2种小白菜对Cd和Zn的吸收动态随生长时间不同而异,Cd积累量随时间延长呈不断增加趋势,而对Zn的吸收积累能力自苗期后缓慢降低。这种差异使小白菜生长后期Cd/Zn比值升高,从而提高了小白菜Cd暴露的潜在风险。此现象在红壤加Cd处理下表现尤其明显。

Pak choi （Brassica chinensis L. ）has been a major diet food in South China. Cd uptake by the plant and Cd concentration in edible leaves of the plant, effect of soil conditions, and plant cultivar, and their interaction are poorly understood. A pot experiment was conducted to explore Cd and Zn uptake during the whole growing period of the plant with and without Cd treatment. Two cultivars of pak choi, Siyueman and Gaogengbai, were grown in two soils （ a Wushantu, Gleyic Stagnic Anthrosols and Hongshanitian, Ultic Stagnic Anthrosols） contrasting in soil chemical properties and soil total Cd and Zn contents. Cd was added at 0 mg · kg^ -1 of soil （ as the control） and 2 mg · kg^ -1, respectively. Pak choi plants were harvested at different growth stages and biomass and Cd and Zn contents of different parts were determined. Uptake of Cd and Zn by the plant was significantly affected by soil type, plant cultivar, and soil Cd dosage, jointly. The studied two cultivars are different in Cd uptake with Siyueman being a cultivar of high Cd affinity and Gaogengbai of low affinity. Under a positive interaction of soil and cultivar, Cd uptake was enhanced by over ten times but Cd/Zn ratio in above ground parts of the plant did not follow the trend of Cd/Zn ratio in total uptake by the plant, for Cd and Zn distribution in different parts varied with cultivar as well as growing stage. The distribution coefficient was 56.3% -71.1% for Cd and 77.6% - 80.6% for Zn. The decreased Cd/Zn ratio under Cd treatment resulted in a decreased Cd/Zn ratio in above ground parts, thus reducing the exposure risk; The dynamics of Cd and Zn uptake varied with growing stage and from cultivar to cultivar. Cd accumulated in the plant steadily with the growing period, while Zn uptake and accumulation turned slightly downwards after the seedling stage, thus leading to higher Cd/Zn ratio in the plant at the harvesting stage and higher risk of Cd exposure. This phenomenon was especially significant in the acid soil.