CH₄ flux and methanogen community dynamics from five common emergent vegetations in a full-scale constructed wetland

To investigate the effects of emergent plants on CH₄ efflux and elucidate the key factors responsible for these effects, annual monitoring of CH₄ emissions and methanogen community dynamics in a full-scale constructed wetland (CW) was conducted. Five emergent plants (Typha orientalis, Cyperus alternifolius, Arundo domax, Iris pseudacorus, and Thalia dealbata) commonly used in CWs were selected for investigation. The greatest CH₄ flux (annual mean 19.4 mg m^-2 h^-1) was observed from I. pseudacorus, while the lowest CH₄ flux (7.1 mg m^-2 h^-1) was observed from Thalia dealbata. The CH₄ flux from five emergent plants showed marked seasonal variation. Total nitrogen (TN) and total phosphorous (TP) were weakly correlated with CH₄ emissions, whereas total carbon (TC) and root biomass of plants were positively correlated with CH₄ emissions. Quantitative real-time PCR (q-PCR) analysis indicated that the gene abundance of eubacterial 16S rRNA, particulate methane monooxygenase (pmoA) and methyl coenzyme M reductase (mcrA) significantly differed among plant species. Differences in TC, root biomass, and dissolved oxygen (DO) caused by plant species were potential factors responsible for differences in methanogens, methanotrophs, and CH₄ emissions. Methanobacteriaceae, Methanoregulaceae, Methanomicrobiaceae, and Methanosarcinaceae were the dominant families of methanogens. The pathways of methanogenesis from the five emergent plants differed, with the main pathway being hydrogenotrophic, while both hydrogenotrophic and acetotrophic methanogens were involved in A. domax. Redundancy analysis (RDA) further indicated that emergent plant types had a profound influence on the methanogenic communities. Taken together, these results suggest emergent plant species can significantly influence CH₄ fluxes in CW through microbial communities, biochemical pathways for methanogenesis, TC, and DO. Furthermore, plant species in CWs should be considered an important factor in evaluating greenhouse gases emission. Finally, it is necessary to effectively manage CWs vegetation to maximize their environmental benefits. Graphical abstract ᅟ.