Study On Microbial Ecological Characteristics And Biological Indexes In Red Soils Polluted By Heavy Metals

In this paper, soil microbial ecological characteristics and their influence mechanism in red soils contaminated with heavy metals were studied using the incubation experiment, and field investigations. Some sensitive microbial ecological indexes and kinetic parameters were brought forward under the single pollution of cadmium or lead, and cadmium-lead-copper-zinc compound pollution ways, respectively, which will be useful reference for bioremediation, environmental quality evaluation and building up alert index systems in red soils polluted by heavy metals. Here the main results of this study are presented:1. Two incubation experiments were conducted to evaluate the effect of cadmium and lead applied singly on soil microbial activities and functional diversity of microbial community in red clayey soil and red sandy soil. The results showed the lower concentration of cadmium or lead helps to increase soil microbial activities, but their higher concentration cause greater inhibitory effect on microbial activities in red soils. Soil microbial biomass carbon, microbial biomass nitrogen, soil basal respiration and metabolic quotient all showed a decreasing trend under more than 15 mg.kg-1 cadmium or more than 200 mg.kg-1 lead, respectively. Soil dehydrogenase, urease and acid phosphotase activities have a significant decrease, and the activities of soil catalase and invertase taking sencond place, while soil protease activities showed stable state. The order of four soil biochemical intensity being sensitive to heavy metal pollution indicated as: nitrification>nitrogen fixation>decomposition of cellulose>ammonification. However, soil microbial biomass C:N ratio increased with the increasing of heavy metals level. Moreover, the effect of heavy metal pollution on soil microbial indexes was significant in red sandy soils. There were significant negative relationships among soil microbial carbon, microbial nitrogen, basal respiration, microbial metabolic quotient, urease activity, dehydrogenase activity, nitrification, nitrogen fixation and cadmium or lead concentration (R0.01=0.765, R0.05=0.632) .There was a close positive relationship between soil microbial biomass C:N ratios and cadmium or lead concentration (R=0.8920). Thus it can be seen that soil microbial biomass carbon, microbial biomass nitrogen, soil microbial biomass C:N ratio and microbial metabolism quotient are very sensitive to heavy metals pollution in red soils. Some soil microbial activity parameters and heavy metals contents were analyzed by principal component method. The results showed that the critical levels of cadmium and lead in red clayed soil and red sandy soil were 15 mg.kg-1 and 0-15.mg.kg-1, 200 mg.kg-1and 200-400 mg.kg-1, respectively.Soil microbial populations and functional diversities of microbial community have changed to some extent under the stress of cadmium and lead pollution. The number of soil bacterial, actinomycetes and fungus in red soils polluted by heavy metals decreased greatly compared with non-polluted soil samples. The order of sensitivity to heavy metals pollution was actinomycetes > bacteria > fungus. At the same time, the result of the functional diversity of soil microbial community indicated that soil microbial metabolism quotient (AWCD), microbial community richness and shannon index all decreased significantly in red soils polluted by cadmium and lead compared with non-polluted soils. These results suggested the structure of microbial community have changed, decreased the functional diversity of microbial community, and reduced the microbial number utilizing different carbon resources.In a word, the changing of soil microbial activities and the functional diversity of microbial community reflected to some degree the evolvement law of environmental ecological function of soil contaminated with heavy metals. Simultaneously, some soil microbial parameters were very sensitive to cadmium and lead pollution.2. Two laboratory incubation experiments were carried out to evaluate the influence of accompanyin...