PRESSURIZED VENTILATION IN WETLAND PLANTS

Species of wetland plants that aerate their submerged organs by thermo-osmotic transport of gas have been identified in six genera of the angiosperm families Butomaceae, Nymphaeaceae and Menyanthaceae. Flow rates of 14 ml gas h-1 in the monocotyledon Hydrocleys nymphoides (Humb. & Bonpl. ex Willd.) Buchenau to 5000 ml in the dicotyledon Victoria amazonica (Poepp.) Sowerby are comparable to those rates found in Nelumbo nucifera Gaertn. from the Nelumbonacean family, but an order higher than those in Alnus glutinosa (L.) Gaertn. from the Betulacean family as reported in the literature. The aeration is driven by a pressurization of the gas in the aerenchyma of young floating leaves as a consequence of the physical effect of thermo-osmosis of gases. Differences in the hygrometric state of the leaves and the ambient air affect the flow rates. Increased transpirational cooling of the upper leaf surface seems to give rise to a steeper temperature gradient within the leaf, intensifying the aeration. As these five plant families are not closely related, the ability to generate a pressurized ventilation by thermo-osmosis of gas can be seen as a special adaptation of wetland plants to the anoxic environment.