Effects of root exudates on denitrifier gene abundance, community structure and activity in a micro-polluted constructed wetland

•Exudates acted as endogenous carbon sources in micro-polluted CW.•Exudates and microorganisms varied significantly among plant species and seasons.•Denitrifier gene abundances were significantly affected by sucrose and glucose.•Microbial communities were significantly affected by sucrose and oxalic acid.

In micro-polluted constructed wetland (CW), the low pollutant concentrations and the low COD/N ratios (chemical oxygen demand: total nitrogen in influent), make the biological treatment more difficult. It is expected that root exudates drive microbial-based transformations within plant rhizosphere. In this research, the roles of root exudates of three aquatic plants (Phragmites australis, Typha angustifolia and Cyperus alternifolius) in improving the growth of heterotrophic denitrifying bacteria were determined in a micro-polluted CW. In studied root rhizospheres, the total organic carbon (TOC) released from the plant roots varied significantly among plant species and seasons; the average TOC ranged from 0.1715 to 0.9221 mg g− 1 root DM d− 1, which could fuel a denitrification rate of approximately 156-841 kg NO3−-N ha− 1 year− 1 if all were used by the denitrifying bacteria; the abundances of nirK- and nirS-encoding bacteria were significantly influenced by the concentration of sucrose and glucose (0.869 ≤ r ≤ 0.933, p < 0.05), and microbial community richness and diversity had response to root exudates. The results revealed that root exudates can act as endogenous carbon sources for heterotrophic denitrifying bacteria and ultimately determine the microbe distribution patterns in micro-polluted CW.

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