Abstract: Lakes are an important source of atmospheric methane (CH₄). However, the impacts of plant types and alien plant invasion on CH₄ emissions in lakes are insufficiently investigated. In this study, four sites including open water, floating plant (Trapa natans), emergent plant (Zizania latifolia), and invasive plant (Eichhornia crassipes) regions were selected in the Honghu Lake in the middle reaches of the Yangtze River. The concentration of CH₄ was measured using a floating chamber and gas chromatography method from May to October, 2022. There were temporal variations of CH₄ emission fluxes at the four sites. The CH₄ emission fluxes ranged from 0.10 to 136.12 mg·m^-2·h^-1, with the peak values presenting in summer or autumn. The mean CH₄ emission fluxes were 1.68, 4.52, 4.58, and 28.59 mg·m^-2·h^-1 at the open water, floating plant, emergent plant, and invasive plant sites, respectively. The CH₄ emission fluxes of three sites with plants were 2.7 to 17 times than that of the open water. The CH₄ emission fluxes from the site with invasive plant was 6.2, 6.3, and 17 times that of the emergent plant, floating plant, and open water sites, respectively. These results could be attributed to the massive plant biomass, more effective plant-mediated transport of CH₄, and higher soil organic carbon content in the invasive plant site. The plant-mediated transport of CH₄ at the three sites dominated by Zizania latifolia, Trapa natans, and Eichhornia crassipes were 0.02, 0.23, and 0.25 mg·m^-2·h^-1, respectively, indicating that Eichhornia crassipes was most efficient in CH₄ transport. Our results suggest that CH₄ emission fluxes derived from the invasive plants would be strengthened in the Honghu Lake in the middle reaches of the Yangtze River, which could be a positive feedback on climate change.

Key words: lake wetland, methane emission, plant type, plant invasion