Stems of Phragmites australis are buffering methane and carbon dioxide emissions

Internal concentrations in the culm nodes of Phragmites australis and fluxes of methane (CH₄) and carbon dioxide (CO₂) were recorded in the treatment bed of constructed wetland (CW) with subsurface wastewater horizontal flow. Fluxes of CH₄ and CO₂ from the CW treatment bed were in ranges of 0 to 490 μmol m^-2 h^-1 and from 0 to 4499 μmol m^-2 h^-1 for CH₄ and CO₂, respectively. The highest CH₄ soil fluxes were recorded in the unvegetated coarse gravel inflow zone of the CW treatment bed. The nearby inflow zone exhibited the highest CO₂ fluxes. Internal culm node concentrations of CH₄ and CO₂ were related to oxygen (O₂) stem concentrations and environmental conditions during diurnal courses. The concentrations of CH₄ and CO₂ gases were significantly correlated and opposing O₂ concentrations. Culm node parameters and shoot density of P. australis influenced internal gas concentrations and the buffering of CH₄ and CO₂ emissions. The effect of buffering CH₄ emissions is distinctive in the outflow zone of the treatment bed and is less important in the highly polluted inflow zone of the CW. Buffering of CH₄ and partially also CO₂ emissions by stems of P. australis is a process which affects the diurnal dynamics of CH₄ and CO₂ fluxes from common reed wetlands.