Vallisneria natans decreased CH4 fluxes in wetlands: Interactions among plant physiological status, nutrients and epiphytic bacterial community

Abstract

Submerged macrophytes provide niches for epiphytic microbes (including aerobic methanotrophs) growth. However, little is known about the impacts of submerged macrophytes growth status and nutrients loadings on methanotroph community and methane release in wetlands. In the present study, methane fluxes, bacterial and methanotroph community in epiphytic biofilm, and environmental parameters were investigated during Vallisneria natans senescence in wetlands under low (VnL) and high (VnH) nutrients for seven weeks. Relative conductivity and concentration of H2O2, total chlorophyll and malondialdehyde were higher in leaves of V. natans in VnH than VnL at the same sampling time. Nutrients loading increased methane fluxes in treatments with or without (Control) macrophytes, while healthy V. natans plants reduced the methane flux and nutrients concentration in water columns. CH4 fluxes were positively correlated to temperature and COD (p < 0.05). Methane oxidation rates were 3.04–31.68 μmol methane mg−1 fresh weight of V. natans leaves - epiphytic biofilm within 1 h. Proteobacteria, Cyanobacteria, Bacteroidetes, Verrucomicrobia, Planctomycetes, Actinobacteria and Acidobacteria were dominant phylum in all epiphytic biofilms. The mean abundances of pmoA/16S rRNA were higher in VnL than VnH. According to Illumina sequencing results of pmoA gene, γ-proteobacteria and α-proteobacteria were the dominant methanotroph class in epiphytic biofilm from VnH and VnL, respectively. Among seven detected methanotrophic genera, Methylomonas was significantly higher in VnH than VnL. Network analysis revealed that there were much closer relationships between the environmental parameters and epiphytic bacterial community in VnH than in VnL. COD and MDA were negatively correlated with Methyloglobulus, Methylosarcina, Methylobacter and Methylocystis, but positively correlated with Methylomonas and Methylosinus. This study highlights that methanotrophs in epiphytic biofilm play important roles in methane-oxidizing, which can be affected by plant physiological status and environmental parameters.