Impact of plant species on spatial distribution of metabolic potential and functional diversity of microbial communities in a constructed wetland treating aquaculture wastewater

• Constructed wetlands treating aquaculture wastewater were studied on field.
• Plant species showed different effect on nitrification and denitrification.
• Bacterial community compositions spatially varied by plant species.
• Radial oxygen loss and root exudates influenced the wetland microbial community.

Two horizontal subsurface flow constructed wetlands, one planted with Iris pseudacorus (HF1) and the other with Phragmites australis (HF2), were built to treat aquaculture wastewater. Pollutants removal, especially the nitrogen removal efficiency, as well as the activities, metabolism, and functional diversities of the microbial communities involved were evaluated under different conditions. NO3−-N was removed in HF1 in all seasons, while it accumulated during autumn and winter in HF2. HF2 was more efficient at removing NH4+-N than HF1 in spring and summer when HRT was above 2 d. Nitrification intensity was higher in HF2, while denitrification intensity was higher in HF1. Biolog-ECO indicated that microbial diversity was higher in HF1 than in HF2, and the structure of the microbial community was more different at the back end and in the lower layer than at other places. These results were further confirmed by qPCR and 454-pyrosequencing. The relative abundances of Nitrospira were highest in back end of the upper layer in HF2, while Denitratisoma, which involves in denitrification, was mainly found in the lower layer of HF1. The results illustrated that the radial oxygen loss from P. australis and root exudates of I. pseudacorus could have an impact on the nitrogen removal efficiency by influencing the development of microbial communities.