Plant functional group diversity in terrestrial ecosystems can strongly influence microbial communities and ecological processes. This was tested in experimental communities containing 1, 2, 3 and 4 plant functional groups including C3 grasses, C4 grasses, legumes and forbs in a full-scale vertical flow constructed wetland (VFCW) fed with post-treated domestic wastewater. The spatial distribution of microbial activities, including basal respiration rate (BSR) and substrate induced respiration rate (SIR), and community-level physiological profiles (CLPP, basing on the BIOLOG Ecoplate technique), together with plant biomass production, were investigated. An increase in plant biomass production (1,208 g m−2) was only observed in the treatment with the highest plant functional group richness, and the BSR also followed a trend similar to plant biomass. The SIR was higher in all planted treatments than in the unplanted treatments, but did not differ significantly across plant functional group richness levels. Utilizations of both carbohydrates and amino acids and the diversity of substrate microbial community computed from average well color development in the Ecoplate followed the SIR dynamic pattern. The average utilization intensity of miscellaneous compounds was higher in all planted treatments than in the unplanted treatment, but decreased significantly with the plant functional group levels. The average utilizations of both polymers and amines/amides were significantly lower in all planted treatments than in the unplanted treatment, but did not differ significantly across the plant functional group levels. The principal components analysis showed that the metabolic profiles separated significantly unplanted treatment from the planted treatments, but did not separated these planted treatments from each other, appearing that the metabolic profiles of microbial community in our wetland only depended on the presence of plants but did not depended on the plant functional group level.Research Highlights► Plant biomass production increased with the plant functional group richness. ► Basal microbial respiration rate positively correlated to plant biomass. ► Utilization of miscellaneous declined with the plant functional group richness. ► Other carbon utilizations only depended on the presence of plants. ► Metabolic profiles of microbial community only depended on the presence of plants.