The importance of dead, still-standing culms of Phragmites australis (Cav.) Trin. ex Steudel as a pathway for exchange of oxygen, carbon dioxide and methane, between sediment and atmosphere, was evaluated during winter. Most of the gas exchange occurs at the basal two internodes of the dead culms. The flux of O2 into the below-ground parts and the emission of CO2 and CH4 into the atmosphere is higher for plants growing on an organic sediment than for plants growing on a sandy sediment. Data suggest that the amount of oxygen entering the below-ground tissue through the lacunae is used mainly to sustain aerobic metabolism of roots and rhizomes. Anaerobic processes are predominant in the rhizosphere, and the culms provide a continuous escape route for methane and carbon dioxide. The oxygen transport capacity of dead culms of P. australis during winter is insignificant in the context of sewage treatment in artificial reedbeds.