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Field sampling and incubation experiment were conducted to investigate differences in microbial metabolic activity and butachlor biodegradation in riparian soils from four different plant communities such as P. australis, A. calamus, and Z. aquatica communities, and a mixed community of P. australis and A. calamus in Chongming Island, China. The results suggested that differences in rhizosphere microbial carbon substrate utilization patterns and enzymatic activities among vegetation types were significant. Catalase activity and fluorescein diacetate (FDA) hydrolysis rate and soil basal respiration (SBR) in the rhizosphere of the mixture of P. australis and A. calamus were 45%, 76%, and 62% higher, respectively, than in the rhizosphere of the pure P. australis community. Community level physiological profiles (CLPPs) via BIOLOG Ecoplates™ indicated that the mixture community of P. australis and A. calamus had the highest sole-carbon-source utilization and functional diversity of microbial community in rhizosphere soil, followed by P. australis, A. calamus, and Z. aquatica. Compared with the rhizosphere soils of the three pure plant communities, the mixture of P. australis and A. calamus displayed a significantly greater butachlor biodegradation percentage in the rhizosphere soil. The half-life for the rhizosphere soil of the mixture community of P. australis and A. calamus were 33, 51 and 57% shorter, as compared to the three pure plant communities, respectively. Our data indicate that vegetation types can exert a great effect on the biodegradation of herbicide in the riparian soil.