Abstract: Soil samples in the rhizosphere of different kinds of continuous cropping black poplar plantation were obtained, and the contents of 5 phenolic acids and their variations were analyzed by HPLC. Results show that P-hydroxybenzoic acid, benzoic acid, vanillin, ferulic acid and cinnamic acid are presented in different accumulation characteristics in the soil of all the continuous cropping types. The content of gross phenolic acids of the second and the third generation of poplar plantation significantly increased 138％ and 642％ respectively, compared with the first generation. The content of ferulic acid increased with a planting generation increase, which was contrary to benzoic acid and cinnamic acid. The experiment of adding five kinds of exogenous phenolic acids to the soil was conducted to study their effects on soil microbes, which shows different effects on soil microbes. In general, with an increasing concentration of the treated exogenous phenolic acids, the amounts of soil microbes first increased, and then decreased. However, P-hydroxybenzoic acid has an inhibitory effect on fungi, actinomycete and ammonifier, but has a stimulating effect on cellulosic bacteria. Vanillin has an inhibitory effect on actinomycetes, and the same effect for ferulic acid and cinnamic acid on cellulosic bacteria.

Key words: soil microbes , phenolic acid, continuous cropping, Populus plantation, high performance liquid chromatography (HPLC)