RHIZOSPHERE MICROBIOLOGY OF CHLORINATED ETHENE CONTAMINATED SOILS: EFFECTS ON PHOSPHOLIPID FATTY ACID CONTENT
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Microbial degradation of chlorinated ethenes (CE) in rhizosphere soils was investigated at seepline areas impacted by CE plumes. Successful bioremediation of CE in rhizosphere soils is dependent on microbial activity, soil types, plant species, and groundwater CE concentrations. Seepline soils were exposed to trichloroethylene (TCE) and perchloroethylene (PCE) in the 10-50 ppb range. Greenhouse soils were exposed to 2-10 ppm TCE. Plants at the seepline were poplar and pine while the greenhouse contained sweet gum, willow, pine, and poplar. Phospholipid fatty acid (PLFA) analyses were performed to assess the microbial activity in rhizosphere soils. Biomass content was lowest in the nonvegetated control soil and highest in the Sweet Gum soil. Bacterial rhizhosphere densities, as measured by PLFA, were similar in different vegetated soils while fungi biomass was highly variable. The PLFA soil profiles showed diverse microbial communities primarily composed of Gram-negative bacteria. Adaptation of the microbial community to CE was determined by the ratio of {omega}7t/{omega}7c fatty acids. Ratios (16:1{omega}7v16:1{omega}7c and 18:l{omega}7t/18:1{omega}7c) greater than 0.1 were demonstrated in soils exposed to higher CE concentrations (10-50 ppm), indicating an adaptation to CE resulting in decreased membrane permeability. Ratios of cyclopropyl fatty acids showed that the vegetated control soil sample contained the more » fastest microbial turnover rate and least amount of environmental stress. PLFA results provide evidence that sulfate reducing bacteria (SRB) are active in these soils. Microcosm studies with these soils showed CE dechlorinating activity was occurring. This study demonstrates microbial adaptation to environmental contamination and supports the application of natural soil rhizosphere activity as a remedial strategy. « lessAn attempt was made, using the soil-washing box technique, to obtain detailed information about the initiation of the rhizosphere mycoflora of dwarf bean seedlings.Tabulated information of the fungi isolated from washed non-rhizosphere soil and washed rhizosphere soil from plants during the first 20 days after seed germination is presented together with data of the fungi isolated from the waters in which these soil samples were washed. These data are discussed in relation to previous observations of fungi isolated from rhizospheres by other methods.The results obtained revealed that in the early days after seed germination the rhizosphere mycoflora was qualitatively similar to that of the non-rhizosphere soil. However, a number of distinct differences were discernible between the rhizosphere and non-rhizosphere populations even at these early stages of plant growth, namely that Cylindrocarpon radicicola, Humicola grisea, and a sterile sclerotial form (W1) were isolated with increased frequency from the rhizosphere, whereas Trichoderma viride was consistently isolated less frequently from the rhizosphere than from non-rhizosphere soil.
Trichoderma viride
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The changes of rhizosphere affected by the rhizosphere microbe was studied.With the contribution of root oxygenation,the soil oxidation-reduction potential maintained at the +100mV in rhizosphere,while the non-rhizosphere maintained negative.Therefore,nitrobacteria and nitrosamines in the rhizosphere have more quantities than those in the non-rhizosphere.The result indicate that the reed had positive effect on the rhizosphere microbe and almost all of microbes were more in quantities than in the non-rhizosphere.It also showed that the pH of the rhizosphere is lower than the non-rhizosphere,and the raise of the soil breathe intensity showed the increase of the microbe activities in the rhizosphere.
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The rhizosphere and bulk soil of Amorpha fruticosa established in different years were studied.Available phosphorus(P),total P and P fractions were analysed using the method of Hedley which was a soil P classification method revised by Tiessen.Available P levels in the rhizosphere were higher than those out of the rhizosphere.The Y60 had the highest inorganic P content than the other except for H2O-Pi and Conc.HCl-Pi.The NaHCO3-Pi,NaOH-Pi,NaHCO3-Po,NaOH-Po,and Conc.HCl-Po in the rhizosphere were higher than those in bulk soil in different aged Amorphaexcept for NaHCO3-Po in Y28.Available P in the rhizosphere had a significant relationship with Dil.HCl-Pi and Conc.HCl-Po.H2O-Pi and total P had a significant relationship.Available P and pH in the rhizosphere and out of the rhizosphere did not have a significant relationship with total P in the rhizosphere.
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Heterogeneity of phospholipid fatty acids contained in rice plantand their endophyte were analyzed by the modified method of phospholipid fatty acids.The results revealed that phospholipid fatty acids of straight chain phospholipid fatty acid such as 20:0,12:0,16:0,18:0 and unsaturated phospholipid fatty acids such as 18:3ω6с(6,9,12),19:0 CYCLOω8с,a17:0,i16:1 H,16:0 N ALCOHOL,15:1ω6с,i15:0 3OH were found both in rice plants and the endophytes,however,the amounts of the phospholipid fatty acid in rice plant were all less than 30μg/g compared to that of more than 30 ug/g in the rice endophytes.The other 22 phospholipid fatty acids were only detected in the rice endophye,for example i20:0,20:1 ω9с,12:0 3OH,the amounts of them were arranged from 0.91~11481.25 μg/g.The contents of the phospholipid fatty acids from the endophytes in different rice were different and they represented to the multiple distribution that meant the definite phospholipid fatty acid distributed in the endophytes in more than one rice variety and the single distribution that meant the definite phospholipid fatty acid distributed in the endophytes in only one rice variety.The correspondence analysis of the phospholipid fatty acids from endophytes showed that corresponding distances of the phospholipid fatty acids were related with the heredity in rice varieties.Loading chart of correspondence analysis displayed that phospholipid fatty acids were multiple distribution when their corresponding distances were longer than,contrary to that,they were single distribution.It is shown that the distribution of phospholipid fatty acids of endophytes were relation with the hereditary of rice.
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In this paper, Total P, Inorganic P, Organic P, Available P and Soil pH in rhizosphere and non-rhizosphere soil of Elaeagnus.mollis were calculated and analyzed by soil P analysis methods. The results show that in Elaeagnus.mollis soil the Total P concentration in rhizosphere was similar to non-rhizosphere. Available P and Inorganic P concentration in rhizosphere were a bit higher than that in non-rhizosphere. Organic P concentration in rhizosphere were a bit lower than that in non-rhizosphere. But there was no significant difference. The correlation between each ingredient of Inorganic P and available P was compared, and found that the relative coefficients of both rhizosphere and non-rhizosphere did not get a significant level. Except Fe-P, the other ingredient concentrations in rhizosphere were little higher than that in non-rhizosphere. The pH in the soil of Elaeaqnus.mollis was smaller in rhizosphere than that in non-rhizosphere, and both of them were somewhat alkali. That is indentical with the high content of Ca-P.
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In the present experiment, the distribution characteristics and availability of inorganic phosphorus fractions in the rhizosphere and non-rhizosphere soil of Populus deltoides cv. 'lux' were investigated. The results showed that (1) Available P was accumulated clearly in the rhizosphere of 3,5 and 11 year-old stands and the accumulation rates were 44%, 96% and 574%, respectively; (2) The contents of Ca 2-P in the rhizosphere of 3,5 and 11 year-old poplar were higher than those in the non-rhizosphere,and the rhizospheric effects (R/S) were 2.15, 2.59 and 5.54, respectively; (3) In the rhizosphere of 5 and 11 year-old poplar, Ca 8-P was accumulated, whereas Ca 10 -P was depleted clearly and the decrease of Ca 10 -P corresponded with the changes of available P, suggesting a stronger consumption in older stands for the P-activation from Ca 10 -P to more available P;(4) There was no obvious difference in Al-P, Fe-P and O-P between rhizosphere and non-rhizosphere soil.
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