The effect of heavy metals on total soil microbiological activity in lettuce

In industrialized countries contamination of soil with a variety of heavy metals has become very common. Microorganisms connect the soil and the plant, and present an important indicator of change in soil biological activity. A trial with lettuce was established in a greenhouse with chernozem soil. After em (21 days) the soil was treated with 10(-3), 10(-5) and 10(-7) M solutions of Pb2+, Cd2+, Mo6+ Ni2+. The study included a determination of the total number of bacteria, ammonifiers, azotobacter, fungi and actinomycetes. Also determined was protease activity as well as dehydrogenase activity, which is an indicator of the total oxidation-reduction processes in the soil. Heavy metals were shown to have a varying effect on the number and enzymatic activity of microorganisms, depending on the concentration and the parameters under investigation, as well as on the element applied. The effect of Pb and Cu on the number and activity of microorganisms was mostly inhibiting, especially when the rates were high (10(-3)). All four elements reduced the total number of bacteria and fungi. The application of heavy metals inhibited dehydrogenase activity, whereas that of protease was reduced, in the case of the highest concentrations, by as much as 25%.