Effect of submerged plant species on CH4 flux and methanogenic community dynamics in a full-scale constructed wetland

Annual monitoring of CH4 and associated microorganisms from four submerged plant species (Potamogeton crispus, Ceratophyllum demersum, Myriophyllum spicatum and Hydrilla verticillata) was conducted in a full-scale constructed wetland (CW). Plant species had a significant impact on CH4 emissions. The highest CH4 flux (5.7 mg m−2 h−1) came from P. crispus, and the lowest flux (1.6 mg m−2 h−1) was from M. spicatum. The dissolved oxygen (DO) and nitrogen of the rhizosphere was significantly affected by plant species, which were the most important factors affecting CH4 flux and methanogenic communities. Changes of DO level caused by plant species were more significant than temperature changes. Real-time quantitative PCR (q-PCR) analysis showed that the number of methanogens and methanotrophs varied with plant species and seasons, whereas the total number of eubacteria was less affected (p > 0.05). The variation of TN and NO2-N caused by plant species resulted in the differentiation of methanogen populations. Each plant species was characterized by a specific group of methanogens. Illumina sequencing showed that the dominant methanogenic populations from P. crispus and C. demersum were hydrogenotrophic archaea of the Methanoregula, while those from M. spicatum and H. verticillata were hydrogenotrophic archaea of the Methanobacterium. Both plant species and seasons affected the percentage of acetoclastic archaea of the Methanosarcina and Methanosaeta. This study indicates that the submerged plant species are important parameters in the production of CH4 emissions in CWs. The proper arrangement of submerged plant species in CWs is vital to maximize the environmental benefit.