中文摘要：

选取北京城郊5个区县土壤为研究对象,通过急性毒性试验,研究了土壤外源镉（Cd）对大麦毒性的影响。结果表明,5个采样点土壤的大麦根伸长与土壤中总Cd和有效态Cd含量的变化趋势均符合剂量效应关系,基于土壤总Cd的EC50（使大麦根伸长降低至对照一半时土壤中的Cd浓度）和有效态Cd的EC50分别变化了1.75倍和1.65倍,基于总Cd和有效态Cd的EC10（大麦根伸长相对对照降低10%的土壤Cd的浓度）分别变化了2.73倍和2.21倍。基于总Cd的EC50最低值出现在阳离子交换量（CEC）最小的丰台土壤,而最高值出现在有机质含量最多的灵山土壤。土壤有效态Cd含量与大麦根伸长的剂量效应关系优于土壤总Cd,用土壤中Cd的有效态表征Cd的生态风险更准确。

英文摘要：

The soil samples from five districts of the suburb Beijing were collected to investigate the response of barley root to metal stress simulated by soil amendment with Cd chlorides by acute toxicity test. The results showed that not only between the total content of Cd and the barley root elongation but also between the extractable Cd and the barley root elongation had a significant dose effect. The toxicity threshold of EC50（as defined as effective concentration of added Cd causing 50% inhibition） that based the total Cd and the extractable Cd content varied 1.75-fold and 1.65-fold separately; EC10（as defined as effective concentration of added Cd causing 10% inhibition） varied 2.73-fold and 2.21-fold separately. The lowest value of EC50 based on the total Cd content appeared in the Fengtai soil, which had the weakest cation exchange capacity（CEC）, and the highest value appeared in the Lingshan soil, which contained the highest amount of organic matter. The extractable Cd and the barley root elongation tended to have a better correlation than the total content of Cd and the barley root elongation, making the contents of extractable Cd indicate the ecological risk more accurately.