Influences Of PAHs On Microbial Communities And Enzyme Activities In Four Greening Trees Potted Soils

Polycyclic aromatic hydrocarbons (PAHs), composed of two or more fused aromatic rings, are ubiquitous, bioaccumulative, and persistent pollutants. With rapid population expansion and concurrent urban and industrial development in recent years, contamination of PAHs in the environment has great impacts on human beings and ecosystems and it has been a serious public health problem. Cinnamomum camphora, Magnolia grandiflora, Koelreuteria bipinnat, Liriodendron chinense, which are important trees for green-gardening in south of China, are widely used in urban and have potential for further development.By pot experiment in greenhouse, the soils of Cinnamomum camphora, Magnolia grandiflora, Koelreuteria bipinnat, Liriodendron chinense seedlings are treated without diesel oil addition (control) and at three diesel concentrations (2g·kg-1 (L1),10 g·kg-1 (L2) and 50g·kg-1(L3)) to stimulate different levels of PAHs pollution. The soil microbes, catalase, phosphatase and polyphenol oxidase are investigated for one year, so as to provide theoretic evidence for screening of good trees which have great effect on removal of PAHs in soil.(1) With the increase of PAHs initial concentration, PAHs content at each stage in the soils of four tree species is increasing. PAHs content in the same treated soils is decreasing with time. Through the regressive analysis on soil PAHs content and days, it is suggested that Cinnamomum camphora has the best effect to remove PAHs, second is Magnolia grandiflora, third is Koelreuteria bipinnata, and Liriodendron chinense is the last. Cinnamomum camphora, Magnolia grandiflora, Koelreuteria bipinnat, Liriodendron chinense would respectively spend 938 days,1201 days,1410 days,1506 days to make soils clear.(2) The populations of the three soil microorganisms of four tree species are in the following order:bacteria>actinomyces> fungi. The populations of soil microbes are affected by PAHs content, plant types, time and so on.The numbers of bacteria, fungi, actinomyces and total microbes in PAHs polluted soils of Cinnamomum camphora and Magnolia grandiflora are lower than that in control soils. The numbers of bacteria, total microbes in PAHs polluted soils of Koelreuteria bipinnata are higher than that in control soils, while Liriodendron chinense is the opposite. The number of fungi in polluted soils of Koelreuteria bipinnata and Liriodendron chinense are higher than that in control soils; the numbers of actinomyces appear that L1>CK>L2>L3.From October,2006 to October,2007, the quantity of bacteria and total microbes in control soils increase at first, then decrease gradually and there is a peak value in April, while those in polluted soils take on earlier or later than CK, which mainly occur in January or July.The quantity of fungi in control soils of Cinnamomum camphora, Magnolia grandiflora, Liriodendron chinense have the same trends with bacteria by time. The most of fungi in control soils of Koelreuteria bipinnata appear in January. The quantities of actinomyces in control soils of four trees have the peak value in January, while it is in April in polluted treatment.(3) Soil enzyme activities have diversities due to the different PAHs content, plant types, time and so on.Catalase activities in polluted soils of Magnolia grandiflora, Koelreuteria bipinnata, Liriodendron chinense are stronger than those in control soils. Catalase activities of Cinnamomum camphora are L3=CK>L1>L2. Phosphatase activities in polluted soils of four tree species are stronger than those in control soils. Polyphenol oxidase activities in polluted soils of Koelreuteria bipinnata, Liriodendron chinense are weaker than those in control soils, and the order of Cinnamomum camphora is L1>CK>L2>L3, and that of Liriodendron chinense is L2>L1>CK>L3.Catalase activities in control soils take on a single peak curve over time, and the peak value occurs in July; those of Liriodendron chinense take on a double peak curve, and the peak value occurs in January and July. Soil catalase activities in polluted treatment appear a double peak curve and the peak value is in January and July; catalase activities in L3 treated soils of Magnolia grandiflora and Liriodendron chinense appear a single peak curve, and the peak value is in July.Phosphatase activities in control soils of Cinnamomum camphora and Magnolia grandiflora decrease with time, and those of Koelreuteria bipinnata and Liriodendron chinense descend from October,2006 to April,2007, ascend from April to July, and then descend. Phosphatase activities in polluted soils of four tree species also appear decrease at first, then increase and decrease at last, and January and July are the turning points. There is a little increasing trend from January to July for. phosphatase activities in lower polluted soils of Koelreuteria bipinnata, and that in higher polluted soils of Koelreuteria bipinnata decline slowly.(4) The correlations between soil microbes, enzymes and PAHs are different with plant types. The correlative analysis shows it is negatively correlated between fungi, actinomyces and PAHs, while it is positively correlated between phosphatase activities and PAHs. Therefore, fungi, actinomyces and phosphatase are suggested as the biological indicators of soil PAHs pollution. Besides, there are significant correlations between phosphatase and polyphenol oxidase activities and microbes.