Interactive effect of dissolved organic matter and phenanthrene on soil enzymatic activities

The investigation of dissolved organic matter （DOM） on urease, catalase and polyphenol oxidase activity in a phenanthrene （Phe）- contaminated soil was conducted under laboratory incubation conditions. Values of soil enzymatic activity depended mainly on incubation time. In the initial 16 days, urease activity increased, and was followed by a decrease. In the initial 8 days, catalase activity decreased and then increased. Variation of polyphenol oxidase activity was just the reverse of catalase activity. After 30 days of incubation, no pronounced difference among treatments with Phe, Phe and DOM, and control were detected in urease, catalase and polyphenol oxidase activity. Phe might inhibit urease and catalase, and stimulate polyphenol oxidase. DOM could improve inhibition of Phe in soil urease and catalase activity during the initial period of applying DOM. Nevertheless, DOM had no significant effect on polyphenol oxidase activity in the Phe contaminated soil. There was a negative correlation between catalase and polyphenol oxidase （r = -0.761＊＊＊）, and catalase and urease （r = -0.554＊＊）. Additionally, a positive correlation between polyphenol oxidase and urease was also detected （r = 0.701＊＊＊）. It is implied that the formed DOM after application of organic wastes into soils may counteract the inhibition of polycyclic aromatic hydrocarbons in soil enzyme activities.