崇明东滩湿地土壤中Cr3+、Pb2+和Cd2+对硝酸还原酶的Hormesis效应

为揭示典型滨海湿地土壤中重金属对土壤酶的低剂量兴奋效应(Hormesis),以崇明东滩湿地为对象,采集土壤样品,分别添加不同剂量的Cr³⁺(0、0.5、5.0、50.0、500.0、5 000.0 mg/kg)、Pb²⁺(0、10、30、50、100、300、500 mg/kg)以及Cd²⁺(0、0.1、1.0、5.0、10.0、100.0 mg/kg),观测土壤硝酸还原酶(NR)活性随时间(0、6、12、24、48、72、120 h)的变化特征。结果表明:与对照(重金属添加量0 mg/kg)相比较,低剂量Cr³⁺(0.5～5.0 mg/kg)、Pb²⁺(10.0 mg/kg)和Cd²⁺(0.1 mg/kg)均使NR活性显著升高(P<0.05),剂量效应曲线表现出明显的倒“U”形。这表明,Cr³⁺、Pb²⁺和Cd²⁺与湿地土壤NR活性之间存在Hormesis剂量效应关系。刺激效应出现的时间分别为培养后的6～72 h(Cr³⁺)、24～120 h(Pb²⁺)和6～48 h(Cd²⁺),幅度变化在56.4%～107.4%之间。因此,低剂量重金属对NR活性的刺激作用可能进一步影响湿地土壤硝态氮的还原过程,建议对崇明东滩湿地土壤中低微量重金属的环境影响进行系统评估。

Hormetic effects of Cr3+, Pb2+and Cd2+on nitrate reductase in soils in Chongming Dongtan wetlands

The objective of this study is to discover the hormetic effects(a biphasic dose-response characterized by a low dose benefit and a high dose inhibition)between heavy metals and soil enzyme in a typical wetland. Soil samples were taken from Chongming Dongtan, a wetland in the Yangtze River Delta of China. The activities of nitrate reductase(NR)in soils were examined at 0, 6, 12, 24, 48, 72 and 120 hrs incubation in the presence of Cr³⁺(0.0, 0.5, 5.0, 50.0, 500.0 and 5 000.0 mg/kg), Pb²⁺(0, 10, 30, 50, 100, 300 and 500 mg/kg)and Cd²⁺(0.0, 0.1, 1.0, 5.0, 10.0 and 100.00 mg/kg), respectively. Results showed that low dosages of Cr³⁺(0.5-5.0 mg/kg), Pb²⁺(10.0 mg/kg)and Cd²⁺(0.1 mg/kg)significantly enhanced NR activities comparing with that of the control(0.0 mg/kg metal ions added)(P<0.05), showing a typical inverted U-shaped dose-response curve, respectively, which indicated that a hormetic dose-response relationship existed between the three metals and NR in soils. The hormetic effects occurred at time of 6-72 h(Cr³⁺), 24-120 h(Pb²⁺)and 6-48 h(Cd²⁺)incubations, respectively, with the maximum stimulatory response of 56.4%-107.4% greater than the control. Therefore, the hormetic effects imply that the enhanced NR activities possibly affect nitrate reduction in wetland soils. It is very necessary to define and evaluate the effects of low dose heavy metals on soil functions in a wetland in the future.