| Hormetic effect is a phenomenon of low-promotion and high-inhibition in toxicology,which is the stimulatory effect of organism to low-dose contamination,and the inhibited response of organism to high-dose contamination.At present,the study of Hormesis at the soil system scale is concerned greatly.Hormetic effects of heavy metals and soil enzymes have been found already.The background concentrations of heavy metals in soil can significantly affect the expression of Hormetic effects since it captured the expression at low-dose range.On the other hand,the distribution of heavy metals in different particle-size fractions in soils at specific background concentrations,which is an important factor in the expression of Hormetic effects.We taken Dongtan soil samples as the object,by using the methods of low energy ultrasound and the second generation high throughput sequencing,and studied that(1)The dose-response effects between Cd and soil alkaline phosphatase(ALP)by adding different doses of CdCl2 solution.(2)The changes of effects and the mechanisms of Cd and soil ALP under different background concentrations which were 0(bulk soil,BS),0.003,0.03 and 3.0 mg/kg,respectively.(3)The Hormetic effects and mechanism of Cd and ALP activity in different particle-size fractions were studied.The soil was separated into 0.1-2 ?m,2-63 ?m,63-200 ?m and 200-2000 ?m by low energy ultrasonic method.The study of Hormetic effects of Cd on alkaline phosphatase in different background concentrations and particle-size fractions of Dongtan wetlands,providing a theoretical basis for studying the Hormetic effects on soil enzyme scale.The main findings and conclusions were as following:(1)The inverse U-shaped dose-response relationship between Cd and soil ALP.The soil ALP activity was 28.7-53.6% higher than that of control at the doses of 0.003-0.3 mg/kg Cd added in soils(P<0.05).When Cd exceeded to 3.0 mg/kg,the soil ALP activity was not significantly different compared with the control.The soil ALP activity was significantly inhibited at the dose of 30.0 mg/kg Cd.(2)The Hormetic effects of Cd and soil ALP was closely related to the interaction time of Cd in soil under different background concentrations.After 7 days of culture,the Hormetic effect of Cd and soil ALP was expressed at the background concentration of 3.0 mg/kg,with the stimulatory amplitude of 13.29-39.00%.After 7 days of culture,the Hormetic effects of Cd and soil ALP were expressed at the background concentration of 3.0 mg/kg,with the stimulus amplitude of 13.29-39.00%.The Hormetic effect of Cd and soil ALP was expressed at the background concentration of 0.003 and 0.03 mg/kg,with the stimulus amplitude of 11.07-24.90% and 13.95-17.15% respectively after 60 days of culture.After 90 days of culture,the Hormetic effect of Cd and soil ALP was expressed at the background concentration of 0.003 mg/kg,with the stimulus amplitude of 11.12-17.40%.With interaction time between Cd and soil interaction time for substantially longer,the Hormetic effects of Cd and soil ALP was more easily expressed at low background concentrations.In the presence of Cd,the bacterial communities,Gammaproteobacteria at the class level,Flavobacteriales and Alteromonadales at the order level,Flavobacteriaceae at the fimily level,Marinobacter at the genus level are obvious dose-response effects.(3)For different particle-size fractions of soil,the ALP activity was 72.3-118.6% higher than that of control with the addition of 0.3-3.0 mg/kg Cd in the 2-63 ?m fraction(P<0.05).In the 63-200 ?m fraction,the ALP activity was 36.4-66.1% higher than that of control at the doses of 0.003-0.3 mg/kg Cd added in soil(P<0.05).0.1-2 ?m and 200-2000 ?m fractions were not existing dose-response effects.The main expression vectors of Hormetic effects between Cd and soil ALP are 2-63 ?m and 63-200 ?m fractions.All of these bacterial communities,Bacteroidetes at phylum level,Flavobacteriia at class level,Flavobacteriales and Cytophagales at order level,Flavobacteriaceae at family level,Gillisia at genus level in 2-63 ?m fraction,Cytophagaceae at family level,Pontibacter at genus level in 63-200 ?m fraction,have obvious dose-response effects to Cd. |
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