Mixed culture of plants improved nutrients removal in constructed wetlands: response of microbes and root exudates

Root exudates are determined by plant species configuration and affect microbial community, which in turn affect purification efficiency of constructed wetlands (CWs). However, it is not well understood how the plant configuration affects CWs purification efficiency through specific root exudates. Herein, four mixed culture CWs were constructed, CW-G3 with Iris pseudacorus , Iris sibirica , Juncus effusus , and Hydrocotyle vulgaris showed the optimal diversity nutrients removal efficiency (TN: 94.2%, TP: 82.9%, COD: 74.7%). Highly increased antioxidant enzymes (peroxidase and catalase) reduced photosynthesis-negative enzyme (malondialdehyde) activity of plants in CW-G3, which ensured oxygen (O 2 ) and organic carbon (OC) production and successfully released to rhizosphere by well-developed root aeration tissues. Further, plant configurations resulted in diversity microbial communities, CW-G3 enriched higher abundance of genus Saccharimonadales and Flavobacterium , which benefited nitrogen removal. More importantly, as OC, higher contents of maltose in CW-G3 (6.6 ~ 11.1 folds of that in other three CWs), as well as lauramide, choline, triethylamine and urocanic acid contributed to microbial denitrifying. Differently, higher contents of unsaturated fatty acids linoleic acid and oleic acid in other three CWs inhibited their microbial nitrifying, rather than utilized by bacteria as OC. Co-occurrent network results also proved the interactions between root exudates and functional bacteria. Thereby, plant configuration in CW-G3 provided higher O 2 and OC contents for bacteria, and reduced nitrifying inhibitors, which contributed to higher purifying efficiency. The study promoted the understanding about root exudates’ effects on bacteria through plant configurations, and improved the purification efficiency of CWs.