Floating plants reduced methane fluxes from wetlands by creating a habitat conducive to methane oxidation

Wetlands are one of the important natural sources of atmospheric methane (CH₄), as an important part of wetlands, floating plants can be expected to affect methane release. However, the effects of floating plants on methane release are limited. In this study, methane fluxes, physiochemical properties of the overlying water, methane oxidation potential and rhizospheric bacterial community were investigated in simulated wetlands with floating plants Eichhornia crassipes, Hydrocharis dubia, and Trapa natans. We found that E. crassipes, H. dubia, and T. natans plants could inhibit 84.31% - 97.31%, 4.98% - 88.91% and 43.62% - 92.51% of methane fluxes at interface of water-atmosphere compared to Control, respectively. Methane fluxes were negatively related to nutrients concentration in water column but positively related to the aerenchyma proportions of roots, stems, and leaves. At the same biomass, root of E. crassipes (36.44%) had the highest methane oxidation potential, followed by H. dubia (12.99%) and T. natans (11.23%). Forty-five bacterial phyla in total were identified on roots of three plants and 7 bacterial genera (2.10% - 3.33%) were known methanotrophs. Type I methanotrophs accounted for 95.07% of total methanotrophs. The pmoA gene abundances ranged from 1.90 × 10¹⁶ to 2.30 × 10¹⁸ copies/g fresh weight of root biofilms. Abundances of pmoA gene was significantly positively correlated with environmental parameters. Methylotrophy (5.40%) and methanotrophy (3.75%) function were closely related to methane oxidation. This study highlights that floating plant restoration can purify water and promote carbon neutrality partially by reducing methane fluxes through methane oxidation in wetlands.