不同土层土壤酶活性对重金属汞和镉胁迫的响应

通过室内模拟重金属污染土壤，研究了不同浓度Hg、Cd单一胁迫及Hg＋Cd复合胁迫对不同土层（0-20cm和20-40cm）土壤脲酶、过氧化氢酶和转化酶活性的影响。结果表明，不同土壤酶对Hg和Cd胁迫的响应并不一致，Hg对土壤脲酶和转化酶的影响较大，Cd对过氧化氢酶的作用更显著。转化酶对Hg、Cd胁迫的响应因处理浓度不同而表现为抑制或激活作用。相关分析显示，脲酶活性可作为土壤Hg及Hg＋Cd污染程度的生化监测指标；而过氧化氢酶活性可以作为Cd污染的指标。同一重金属浓度胁迫下，0—20cm土层的土壤酶活性明显高于20～40cm土层的土壤酶活性。Hg、Cd胁迫对0～20cm土壤脲酶和过氧化氢酶的抑制作用小于20～40cm相应土壤酶活性，高浓度Hg和低浓度Cd对0—20cm土壤转化酶表现为抑制作用，而对20-40cm土壤转化酶却表现为激活作用。

Responses of Soil Enzyme Activities in Different Soil Layers to Single and Combined Stress of Hg and Cd

The single and combined effects of two heavy metals（Hg, Cd） applied to 0-20 cm and 20-40 cm soil samples on activities of soil urease, eatalase and invertase were studied. The concentrations of Hg^2＋, Cd^2＋ and Hg＋Cd were 0, 0.312 5, 0.625, 1.25, 2.50 mg·kg^-1, 0, 25, 62.5, 125.0, 187.5 mg·kg^-1, 0, 25.312 5, 63.125, 126.25,190.0 mg·kg^-1, respectively. The three enzymes responded differently to Hg and/or Cd stress, the activity of soil urease was significantly inhibited under Hg stress, Cd showed obvious inhibitory effect on the eatalase, while the change of invertase activity varied with the concentration of Hg and/or Cd. The correlation analysis demonstrated that urease activity may be used as a biochemical indicator for monitoring Hg pollution and compound pollution of Cd and Hg, and soil eatalase activity may be used as a biochemical indicator for monitoring Cd pollution. Under the same concentration of heavy metals, the soil enzyme activity in 0-20 cm soil layer was significantly higher than that in the 20-40 cm Soil layer. The inhibition effects of Hg, Cd on soil urease and eatalase in 0-20 cm were lighter than those in 20-40 cm, which related to the higher organic content in 0-20 cm soil; while, high concentration of Hg and low concentration of Cd could inhibit the invertase activity in 0-20 cm soil but stimulate that in 20-40 cm soil.