The Importance of Water Vapour for the Circulating Air Flow throughNelumbo nucifera

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Abstract
Aquatic vascular plants depend on an adequate oxygen supply in order to maintain growth and reproduction in anaerobic environments. Nelumbo nucifera is able to survive with a gas transport system which supplies oxygen to the roots and rhizomes submerged in the anaerobic sediment. It was possible to demonstrate that this gas transport system is based on a purely physical phenomenon Thermo-osmotic oxygen transport was first demonstrated on fresh leaves with the help of an oxygen-sensitive electrode. A definite enhancement of oxygen flow was obtained through excised leaves when a temperature difference between the ambient and lacunar air was present in light. These leaves were then dried to brittleness and the enhanced oxygen flow was still detectable. This shows that not only photosynthetic oxygen, but also atmospheric oxygen can be transported to the buried organs. The absolute flow of oxygen through dry leaves was much lower than through fresh leaves, but the thermo-osmotic transport of oxygen still functioned. Furthermore, the process of thermo-osmosis need not rely on a difference in humidity between the two sides of a porous partition, but may be linked causally to the temperature difference and the pore size.