Effects Of Traditional And Emerging Pollutants On Soil Biological Processes And Soil Microorganisms

Soil is a complex and dynamic ecosystem, in which biological process is mostly governed by microorganisms. Microorganisms play critical roles in nutrient cycling, maintenance of soil structure, degradation of agrochemicals, and the control of plant and animal pests.In recent decades, a variety of herbicides with diverse compositions and structures have been used to protect crops against weeds in agricultural practices. It has been reported that most agricultural soils in China are treated with herbicides at least once a year. As one of the most common heavy metal contamination in the environment, lead(Pb) pollution has been addressed in the literature because of its high toxicity levels and adverse effects on organism and human health. In addition, nanotechnology has provided a basis for innovation in a wide range of fields and resulted in an exponential increase in products of novel materials. Carbon nanotubes(CNTs) are one of the most promising nanomaterials and have become the subject of numerous investigations in chemical, physical and material science research areas since its discovery. With their expanding role of CNTs in manufacturing, some environmental exposure is raising concerns about their potential environmental risk. The objective of this study was to investigate the impacts of atrazine, Pb and CNTs on the soil microbiota, soil net nitrogen mineralization, soil basal respiration, and soil enzyme activities etc. This study has provided useful information on potential ecotoxicology effects of contamination of atrazine, Pb or CNTs on relative microbial biological process. Major results are listed as follows:(1) Results showed that the notable effects of either or both contaminants on the microbial activity and biological processes. Enzyme activity data demonstrated that the order of sensitivity to contamination was urease > invertase > catalase. Soil basal respiration was strongly stimulated by atrazine / Pb at the early exposure. The combination of atrazine and Pb had a significant inhibition effect on soil net nitrogen nitrification.(2) Denaturing gradient gel electrophoresis(DGGE) analyze show that existence of atrazine or Pb(especially high concentration) in soils reduced microbial diversity(the Shannon–Wiener diversity index lowest H value is 2.23) compared to the control(H=2.59) after incubation. The species richness reduced little over the research time. But soil microbial community was significantly affected by the incubation time after the exposure to atrazine or Pb. Pb accelerated the level of atrazine dissipation. The exposure might stimulate the significant growth of the autochthonous soil degraders which may use atrazine as C source and accelerate the dissipation of atrazine in soils.(3) The first exposure of CNTs lowered the microbial biomass immediately, but the values recovered to the level of the control at the end of the experiment(two weeks later). The addition of SWNTs inhibited the soil net nitrogen nitrification(Rnit) at the begaing of the incubation(0-3 day). However, SWNTs produced a stimulation effect on the Rnit from 3 to 7 days. The effects of MWNTs were contrary to the SWNTs. Rnit generally recovered to the level of the control at the end of the incubation, except for the high concentration of CNTs. The abundance and diversity of ammonium-oxidizing archaea(AOA) were higher than that of ammonium-oxidizing bacteria(AOB) under the exposure of CNTs. The addition of CNTs decreased Shannon–Wiener diversity index of AOB and AOA. Two-way ANOVA analysis showed that CNTs had significant effects on the abundance and diversity of AOB and AOA. Dominant terminal restriction fragments(TRFs) of AOB exhibited a positive relationship with NH4+-N, while AOA was on the contrary. It implied that AOB prefer for high NH4+-N soils whereas AOA is favored in low NH4+-N soils in the CNT-contaminated soil.