Abstract: In this study, we conducted hydroponics and constructed wetlands (CWs) experiments with six assemblages of four plant species. We examined the relationships between rhizosphere microenvironment factors and water quality treatment performance and greenhouse gas (GHG) emission reduction capacity of CWs, to select the plant assemblage that can simultaneously remove pollutants in water and reduce GHG. In the hydroponics experiment, “Lythrum salicaria+Phragmites australis” accelerated plant growth and had the highest rate of radial oxygen loss (ROL) and dissolved organic carbon (DOC). After reaching stability, the CW with “Lythrum salicaria+Phragmites australis” had the highest removal efficiencies of COD (82.8%), TP (59.4%) and TN (68.9%). Moreover, the “Lythrum salicaria+Phragmites australis” had the lowest global warming potential (GWP), with 311.72±0.13 mg·m^-2·h^-1 CO₂eq in hydroponics experiment and 561.80±0.22 mg·m^-2·h^-1 CO₂eq in CWs experiment. High-throughput sequencing results showed that the assemblage “Lythrum salicaria+Phragmites australis” increased microbial richness and diversity, improved the abundance of nirS, nosZ and pmoA, and decreased mcrA abundance in the CW. In conclusion, the assemblage of “Lythrum salicaria+Phragmites australis” could simultaneously achieve higher pollutant removal efficiency and lower GHG emissions, providing a new choice for improving ecological benefits of CWs.

Key words: constructed wetland, plant assemblage, greenhouse gas reduction, radial oxygen loss, microbial community