Effects of arbuscular mycorrhizal fungi on enzymes activity in soils contaminated by phenanthrene and pyrene.

A greenhouse pot experiment was conducted to investigate the effects of arbuscular mycorrhiza (AM) on microbes and soil enzymes in rhizosphere and hyphosphere soil contaminated by phenanthrene and pyrene. The quantities of bacteria, fungi, and actinomyces in both rhizosphere and hyphosphere increased significantly, and the microflora changed with the inoculation of arbuscular mycorrhizal fungi (AMF). The soil contamination of phenanthrene and pyrene with lower concentration clearly stimulated the activity of enzymes including acid phosphatase, polyphenol oxidase and catalase. However, when the contamination dose was higher, their activities were inhibited. Compared with bulk soil, the activity of acid phosphatase in rhizosphere with AMF was decreased by 2.4%～23.1%, and catalase in rhizosphere was decreased by 12.6%～20.3%. By contrast, the activity of polyphenol oxidase in rhizosphere was stimulated except those treatments with high levels of PAH. Polyphenol oxidase activity in hyphosphere was 2.9%～62.9% lower, while acid phosphatase activity was 3.3%～24.0% higher than that in rhizosphere. In general, catalase activity in hyphosphere was higher than that in rhizosphere. In addition, both AM and hypha enhanced the activity of catalase in soils. The enhanced activity of polyphenol oxidase by AM in rhizosphere could be the results of improved plant growth and root activities with AMF inoculation.