Study On Rhizosphere Methane Oxidation Activities Of Landfill Cover Soil

Greenhouse gas, methane, can be oxidized by methane-oxidizing bacteria (methanotrophs) in landfill cover soils. The oxidation activities of these bacteria were affected by several factors, including plant cover. In this study, the population of methanotrophs in landfill cover soil and methane oxidation activities were investigated by using the hungate roll tube method and gas chromatography, and the evolution of methanotrophs community in landfill cover soils were investigated by DGGE of 16S rDNA fragment polymerase chain reaction products.Methanotroph growth and reproduction, in the enrichment culture process, can be divided into 4 phases:adjustment, exponential, stationary, and decline phase. The first 7 days in culture about the density of methane oxidizing bacteria reached a peak into the stationary phase. The amount of methanotroph in the landfills soil ranges from 107 to 10s cfu·g-1 dry soil, the oxidation rate on methane fluctuates between 10-7～10-8 mol-h-1·g-1. The high-to-low order of the average oxidation rate in the soil samples from the different landfills is, Asuwei landfill> Taoshugang landfill 3> Laohuchong landfill> Taoshugang landfill 2> Taoshugang landfill 1> Zhaojiagou landfill.The results showed that the shorter closure time for the landfill, the higher methanotroph population and methane oxidation activities; The vegetation coverage were highly significant negative correlations with methanotroph population and significant negative correlations with methane oxidation activities; there was negative correlation between moisture content and methane oxidation activities; The results also showed that there were no significant correlation between pH, organic matter, NH4+ of landfill cover soils and methane oxidation activities. It was better for methanotrophs to reproduce and oxidizing methane in summer than Spring, but the seasonal and year variations were not in relievo. The methane oxidation activities were positively correlated with the population of methanotrophs, but that was not the only factor to influence the activities.Not the typeⅠmethanotrophs nor the typeⅡmethanotrophs in the cover soils of the same landfill showed high similarity(generally over 60%).The methanotrophs community composition in rhizosphere soil of landfill was higher than bulk soil. The various of Shannon index of methanotrophs in rhizosphere soil of different plants were not obviously, there was a positively correlation between the abundance and Shannon index of both typeⅠand typeⅡmethanotrophs, the abundance of methanotrophs affected the methanotrophs community composition, but not existing significant correlation between them. The methanotrophs community composition was positively correlated with the methane oxidation activities, but was not directly proportional each other, so methanotrophs community composition was not the only factor to influence the methane oxidation activities.Plants could promote the Population, diversity and methane oxidation activity of methanotrophs. The functional plants for methane purification, such as Calystegia hederacea Wall, Conyza Canadensis, Cirsium setosum (Willd.) MB, and Kummerowia striata (Thunb.) Schindl., were suitable as pioneer plant species for revegetation in closed landfills.