Effect Of Organic-heavy Metal Combined Pollution On Rhizosphere Microbial Ecology

Combined pollution caused by organic pollutant and heavy metal is one of the important soil pollution forms. The rhizosphere is a dominant site of microbial activity in soil and whereas it can be shown that soil pollution can influence the function of this comic zone. There is an established need to monitor effects of organic-heavy metal combined pollution on rhizosphere microbial ecology given the soil heavy metal contamination with the simultaneity of organic pollution is an emerging problem. In this paper, the effect of organic-heavy metal combined pollution (PCP —Cu, Pyrene— Cu) on rhizosphere microbial activity and bacterial community were studied using some sensitive microbial ecological indexes such as soil respiration rate, microbial biomass carbon and ecophysiological index. Here the main results of this study are presented:( 1 ) The soil respiration rate and microbial biomass carbon decreased obviously under the PCP pollution stress. Wth the increase of PCP concentration, the microbial biomass carbon decreased deeply and rhizosphere mitigate the detrimental effects of PCP on siol microbial biomass carbon. But at the same concentration Pyrene pollution level, the soil respiration rate and microbial biomass carbon of no-planted soil and rhizosphere of ryegrass and radish were increased. And the increase of rhizosphere is more obvious than no-planted soil. The effects of PCP, Pyrene on the metabolic quotient were different between different plant rhizoshere and no-planted soil.( 2 ) The pollution of copper stimulated the soil respiration rate of no-planted soil. The rhizosphere of ryegrass and radish weakened the stimulation of soil respiration rate under pollution (150mg·kg^-1 Cu and 300mg·kg^-1 Cu) condition. The microbial biomass carbon was restrained under 300mg·kg^-1 Cu pollution stress. The plants had a rhzosphere effect, which lightened the toxicity of copper pollution on rhizosphere microbes.( 3 ) The effect of PCP-Cu combined pollution on respiration rate of no-planted soil and rhizosphere of ryegrass and radish was complex. With the deterioration of PCP-Cu combined pollution, the microbial biomass carbon decreased obviously. Because of rhisozphere effect, the decrease of rhizosphere was not obvious as no-plnted soil. But under the Pyrene—Cu combined pollution, with the aggravation of combined pollution stress,the soil respiration of no-planted and rhizosphere wasenhanced. At the same time, the microbial biomass carbon of no-planted soil and rhizosphere decreased to some extent. PCP-Cu, Pyrene-Cu combined pollution caused the change of metabolic quotient, When Cu existed with organic pollutants together at higher concentration, the soil metabolic quotient of no-planted soil and rhizosphere increased more obvious than control soil.( 4 ) In heavy metals contaminated soil, the copper—toletrant bacterial colony of rhizosphere ryegrass had the largest ecophysiological index and stability. In only heavy metals contaminated soil, the PCP-tolerant bacteria also existed in no-planted soil and ryegrass rhizosphere. After introducing PCP into heavy meals contaminated soil, PCP—toletrant bacterial colony of no-planted soil displayed early and had a higher ecophysiological index than rhizosphere.( 5 ) The microbes that can used pyrene to growth were existed in rhizosphere of ryegrass and radish. After 15 day degradation experiment, the Pyrene of 80 mg·L^-1 can be degraded completely. Because the joint toxicity of PCP-Cu combined pollution to microbes was complex, the growth and degrading ability of the PCP degrading microbes was different.