Assessment of effects of heavy metals combined pollution on soil enzyme activities and microbial community structure: modified ecological dose-response model and PCR-RAPD

Alaboratory study was conducted to evaluate the response of soil enzyme activities (namely dehydrogenase, phosphatase and urease) to different levels of trace element pollution in soil representative area. The improved ecological dose model and random-amplified polymorphic DNA (RAPD) were used to assess soil health. The 50% ecological dose (ED50) values modified by toxicant coefficient were calculated from the best-fit model, and determination values from the regression analysis for the three enzyme activities were studied after the incubation periods. The results showed that the elevated heavy metal concentration negatively affects the total population size of bacteria and actinomycetes and enzymatic activity; dehydrogenase (ED50 = 777) was the most sensitive soil enzyme, whereas urease activity (ED50 = 2,857) showed the lowest inhibition; combined pollution or elevated toxicant level would increase disappearing RAPD bands, and the number of denoting polymorphic bands was greater in combined polluted soils. All three mathematical modified models satisfactorily described the inhibition of soil enzyme activities caused by Cd and Pb, by giving the best fit.