XVI International Botanical Congess

The paper reviews our anatomical and physiological researches on the Grey Mangrove Avicennia marina. This mangrove has extensive cable roots with vertical pneumatophores and a dense mat of fine roots. Gas spaces occupy from about 20% by volume in fine roots to 70% in cable roots. The gas spaces are interconnected and access the atmosphere at low tide through lenticels and 'horizontal structures' (subrisules) on pneumatophores. Gas pressure inside typically falls by a few kPa while the pneumatophores are covered by water at high tide. There is a slight mass flow of air into the root system at the moment the pneumatophores become uncovered as the tide falls. Generally, however, gas exchange between root system and atmosphere is by diffusion. The cable roots store enough oxygen to maintain aerobic conditions throughout high tide.