Plant-driven microbiome reorganization sustains multifunctionality of iron-biochar constructed wetlands under chronic PFOA exposure

Plant capacity to regulate treatment stability and ecological function of iron-biochar (IC) based constructed wetlands (CWs) operated under long-term PFOA exposure remains insufficiently understood. In this study, compared with unplanted system, plant (Iris pseudacorus) increased the dynamic transformation of ammonium and nitrate, limited nitrite accumulation, thus promoting total nitrogen removal, which was, on average, 12.54% higher in planted system. Besides, vegetation increased total phosphorus and chemical oxygen demand removal efficiency by 14.21% and 7.97% on average. These improvements were accompanied by vegetation-associated changes in enzyme activity, including higher dehydrogenase, phosphatase, and nitrate reductase activities during specific periods or in specific layers, greater EPS production, and improved biofilm stability with reduced bio-clogging risk. Microorganism-plant interaction also influenced greenhouse gases (GHG) emission, in which CO2 fluxes were 4.32-71.61% lower in the planted group during most sampling periods, and CH4 emissions and long-term global warming potential were also reduced. Plants also markedly increased microbial richness/diversity and enriched dominant functional taxa. Besides, Dominant genera involved in microbial carbon/nitrogen/phosphorus metabolism, iron/sulfur cycling, electron transfer, PFOA resistance, and decrease of GHG emission risk were enriched in various layers of planted group. Such variation of microbial community resulted from related gene regulation in planted group. Some other indicator bacteria also contributed substantially to optimized microbial community in planted group, including Shewanella, Thiobacillus, and Dechloromonas. These new findings provided preliminary evidence for integrating Iris pseudacorus into IC-based CWs to improve the operational stability of IC-based CWs.