Abstract:Polycyclic aromatic hydrocarbons (PAHs) are a kind of organic pollutants which exist in environments chronically, they are of particular concern because some are potent toxins and some can be highly persistent in the environment, also pose a carcinogenics risk to humans. The aim of this trial was to quantify the responses of soil enzyme activity during the phytoremediation of polycyclic aromatic hydrocarbons(PAHs) under laboratory control. In the experiments 4 tree species including Cinnamomum camphora, Magnolia grandiflora, Koelreuteria bipinnata, Liriodendron chinense, from subtropical China were elected and planted separatedly in the pots in which soils were treated with diesel oil to three concentration levels of PAHs(L1﹤L2﹤L3). Throughout the 180-d experiment of soil phosphatase, polyphenol oxidase and hydrogen peroxidase activity were monitored. Under different concentration of PAHs, the order of phosphatase activity was L2>L3> L1, the order of polyphenol oxidase and hydrogen peroxidase activity was L3> L1> L2. There are difference in enzymatic activities among 4 tree species. Treated with L1, the order of 4 tree species was Liriodendron chinense﹥Magnolia grandiflora﹥Cinnamomum camphora﹥Koelreuteria bipinnata;treated with L2,the order of 4 tree species was Koelreuteria bipinnata﹥Liriodendron chinense﹥Cinnamomum camphora﹥Magnolia grandiflora;treated with L3,the order of 4 tree species Liriodendron chinense﹥Cinnamomum camphora﹥Magnolia grandiflora﹥Koelreuteria bipinnata. The change ratio of polyphenol oxidase and hydrogen peroxidase activity showed significant difference with PAHs concentration. The soil enzymes showed few correlation with soil microbes. The activities of soil polyphenol oxidase and hydrogen peroxidase can be regarded as indexes to assess PAHs contaminated soil.