A BENEFICIAL GAS TRANSPORT SYSTEM IN NYMPHOIDES PELTATA

The aquatic vascular plant Nymphoides peltata (Gmel.) 0. Kunze which inhabits anaerobic environments depends highly on the availability of oxygen for its submerged organs buried in the sediment of the lake. In tracer gas studies, carried out with shaded plants, it is shown that ethane is taken up by one of the youngest leaves in a whorl and transported down the petiole to the axis, returning to the surface via the older leaves. In sunlight, this gas diffusion through the plant is replaced by an effect which enhances the gas movement up to 1,200% due to the increased difference between leaf temperature and the surrounding air (AT = 1.7 K). The temperature difference is accompanied by a pressurization 50 Pascal above ambient inside the aerenchyma of the young leaves. These findings confirm that a pressurized flow-through system is established by N. peltata, whereby the oxygen supply to the rhizomes is improved. The temperature difference derived from irradiation energy initiates a circulating air stream, which transports air from the young leaves through the plant. Enhanced transport of a tracer gas as well as oxygen can be demonstrated by warming an excised young leaf with red-filtered light or warm water. A similar increase in gas transport is not detected through older leaves. The light energy needed to create a temperature difference can be substituted with warm water. Evidence is thus given, which shows that the increased oxygen emission from the petiole of young leaves is independent of photosynthesis. This gas transport is a result of thermo-osmosis under slip-flow conditions (Knudsen diffusion), limiting this effect to a temperature gradient between the surrounding air and the lacunar air of young leaves.