Effects of Cd and Pb pollution on soil enzymatic activities and soil microbiota

Based on a representative sampling method and pot experiment with different concentrations of Cd and Pd, the enzymatic activities (urease, phosphatase, catalase, invertase), population of bacteria, fungus and actinomycete in the soil, the Cd and Pd pollution status of soil samples (from the wastewater-irrigated area of Baoding suburb) were appraised. Unitary linear and nonlinear curve-fitting optimization models were applied in the research, and the relationship between Pb and Cd causing pollution and enzymatic activities of the tested soils were discussed. The research may provide a theoretical basis for protecting the environment in the region of Baiyangdian Lake, Hebei province, prevent soil pollution, and ascertain biochemical indexes, which reflect soil heavy metal pollution levels. The research results indicated that: (1) there was obvious accumulation of Pb and Cd in the wastewater-irrigated area, also the accumulation in wastewater-irrigated soil is more than that in fresh water-irrigated soil, and accumulation on surface layer was more than that in the lower layer. Pb and Cd contents in the tested soils exceeded the standards of soil background values for some major cities at home and abroad and the world soil Cd and Pb contents range. This means that the tested soil had reached a lightly polluted level; (2) there existed an obvious negative correlation between soil enzymatic activities and Pb and Cd contents in wastewater-irrigated soil, where the soil urease and catalase activities decreased obviously with the increase of Pb and Cd contents in soil. Therefore, the urease and catalase can be considered as biochemical indexes that reflect the degree of soil Pb and Cd pollution; (3) the pot experiments indicated that the influence of Cd on soil enzymatic activities was greater than that of Pb. Generally, the effect of Cd on soil phosphatase, urease, catalase is more obvious than that on invertase, while Pb has a more obvious effect on invertase than Cd; (4) pot experiments of triple cropping showed that, Cd and Pb had an obvious inhibiting effect on microbes. The influence sensitivity of Cd and Pb on different microbes was ordered as bacteria > actinomycete > fungus. Cd had a greater inhibiting effect on microbes than Pb, the influence of Cd and Pb on actinomycete and fungus was relatively smaller, therefore, bacteria can be chosen as an important index that reflects the effect of Cd and Pb on microbe sensitivity.