Effects of different emergent macrophytes on methane flux and rhizosphere microbial communities in wetlands

Emergent macrophytes are of great importance for the structure and functioning of wetland ecosystems and play a significant role in environmental improvement, element cycling, and greenhouse gas (GHG) emissions. However, our understanding of how GHG fluxes differ among macrophyte species and its links with the microbial communities remain limited. In this study, we investigated the rhizosphere microbial communities (including total bacteria, methanotrophs, and methanogens) and the GHG fluxes associated with four emergent macrophytes-Phragmites australis, Thalia dealbata, Pontederia cordata, and Zizania latifolia-collected from Xuanwu Lake wetland, China. We observed the highest CH₄ flux (FCH₄) (9.35 ± 2.52 mg·m^-2·h^-1) from Z. latifolia zone, followed by P. australis, P. cordata, and T. dealbata zones (5.38 ± 1.63, 2.38 ± 2.91, and 2.02 ± 0.69 mg·m^-2·h^-1, respectively). Methanogenesis was methylotrophic at all sites, as the ¹³C-CH₄ values were higher than -64 ‰ and the fractionation coefficients were lower than 1.055. We found a positive linear relationship between FCH₄ and the methanogen community, in particular the relative abundances of Methanobacterium and Methanosarcina, indicating that the variations in FCH₄ among the studied macrophyte-dominated zones might be attributed to the differences in rhizosphere microbial communities. The methane emissions in various macrophyte zones might be due to the higher capacity of methanogenesis compared to methane oxidation which was inhibited by nutrient-rich sediments. Our findings provide insights for selecting specific emergent macrophytes characterized by low FCH₄ in wetland ecological restoration.