Terrestrial saltmarsh plants inhabitin flood-prone habitats undergo recurrent and prolonged flooding driven by tidal regimes. In this study, the role of internal plant aeration in contrasting hypoxiclanoxic conditions during submergence was investigated in the two halophytes Linionhan narbonense Mill. and Sarcocornia fruticosa (L.) A.J. Scott. Monitoring of tissue O-2, dynamics was performed in shoots and roots using microelectrodes under drained conditions, waterlogging, partial and complete submergence, in light or darkness. For both species, submergence in darkness resulted in significant declines in tissue O-2 status and when in light, in rapid O-2, increases first in shoot tissues and subsequently in roots. During partial submergence, S. fruticosa benefitted from snorkelling and efficiently transported O-2 to roots, whereas the O-2 concentration in roots of L. narbonense declined by more than 90%, Significantly thinner leaves and articles were recorded under high degree of flooding stress and both species showed considerably high tissue porosity. The presence of aerenchyma seemed to support internal aeration in S. fruticosa whereas O-2 diffusion in L. narbonense seemed impeded, despite the higher porosity (up to 50%). Thus, the results obtained for L. narbonense, being well adapted to flooding, suggests that processes other than internal aeration could be involved in better flooding tolerance e.g. fermentative processes, and that traits resulting in flooding tolerance in plants are not yet fully understood
