中文摘要：

为了明确Cd^2＋、Cr^3＋与碱性磷酸酶（ALP）活性之间的低剂量兴奋效应关系,以崇明东滩湿地土壤为对象,通过添加不同剂量的外源Cd^2＋（Cd Cl2）和Cr^3＋（Cr Cl3）,使土壤中w（Cd^2＋）分别为0、0.001、0.01、0.1、1、5、10、20、100和500 mg·kg-1,w（Cr^3＋）为0、0.5、5、50、100、500和5 000 mg·kg-1,观测土壤ALP活性随时间（0、6、12、24、48、72和120 h）的变化特征。结果表明：（1）培养12 h后,Cd^2＋添加量为1 mg·kg-1时,ALP活性比对照高8.6%（P〈0.05）;当Cd^2＋添加量大于10 mg·kg-1时,酶活性受到明显抑制。Cr^3＋添加量为5 mg·kg-1时,ALP活性比对照显著升高22.8%（P〈0.05）;当Cr^3＋添加量大于100 mg·kg-1时,酶活性显著降低。这表明Cd^2＋和Cr^3＋与ALP之间存在典型的低剂量兴奋效应,但效应的表达与两者接触时间的长短密切相关。（2）以培养24 h的土壤样品为例,Cd^2＋添加量为1和5 mg·kg-1时,ALP的催化效率（Vmax/Km）,即最大反应速率（Vmax）与Michaelis常数（Km）的比值为1.7;当Cd^2＋添加量增加到20 mg·kg-1时,Vmax/Km比降至0.8,而Vmax和Km的值均低于对照。Cr^3＋添加量为0.5和5 mg·kg-1时,Vmax/Km比为1.7;当Cr^3＋添加量增至100 mg·kg-1时,Vmax/Km比降为1.4,但Vmax和Km值均高于对照,这表明重金属与土壤酶之间的低剂量兴奋效应机理可能与其离子特性密切相关。

英文摘要：

To explore low.dose hormetic effects （a biphasic dose.response characterized by a low dose benefit and a highdose inhibition） of Cd2＋ and Cr3＋ on activity of alkaline phosphatase in wetland soil, soil samples were collected from thewetland in Dongtan of Chongming, treated with different doses of Cd2＋ and Cr3＋ , making the samples 0, 0. 001, 0. 01,0. 1, 1, 5, 10, 20, 100 and 500 mg·kg-1 in Cd2＋ concentration and 0, 0. 5, 5, 50 100, 500 and 5 000 mg·kg-1 inCr3＋ concentration, separately, and then incubated for 0, 6, 12, 24, 48, 72 and 120 hrs. After the incubation soil sam.ples were analyzed for activity of alkaline phosphatase （ALP）in soils to determine characteristics of the temporal variationof the activity with the incubation. Results show that after 12 hours of incubation, ALP activity was 8. 6% higher in the soilsamples 1 mg·kg-1 in Cd2＋ concentration than in CK, and was obviously inhibited in the soil samples 10 mg·kg-1 inCd2＋ concentration（P〈0. 05）, while ALP activity was 22. 8% higher in the soil samples to 0？？ 8 in the soil samples 20？？ 0 mg·kg-1 in Cd2＋ concentration with both Vmax and Km being lower than their respectiveones in CK （soil samples 0 mg·kg-1 in Cd2＋ concentration）, and Vmax / Km was also 1？？ 7 in the soil samples 1 and 5 mg·kg-1 in Cr3＋ concentration, and 1？？ 4 in the soil samples 100 mg·kg-1 in Cr3＋ concentration, with both Vmax and Km beinghigher than their respective ones in CK. All the findings indicate that both Vmax and Km fall simultaneously in the presenceof Cd2＋ , but rise simultaneously in the presence of Cr3＋ , and that the mechanism of low？case hormesis existing betweenheavy metals and soil enzymes may be closely related to properties of the heavy metal ions.