PRESSURIZED VENTILATION IN FLOATING-LEAVED AQUATIC MACROPHYTES

Gas through-flow by pressurised ventilation is well known in floating- leaved aquatic plants. The ventilation system operates via different s tructural features in different species: being through rhizomes in Nup har species, is restricted to whorls in Nymphoides, or even individual leaves in Nelumbo. The convective through-flow in these aquatic plant s is the result of a gas-pumping system, commonly powered by solar rad iation, with air influx and pressurisation of the youngest, just emerg ed leaves along positive humidity and temperature gradients between le af aerenchyma and the ambient atmosphere. It improves the internal aer ation of submerged plant organs, has high physiological significance t o the plant, and confers beneficial effects on the ecosystem. Since th e acquisition of gas through-flow systems is not restricted to closely related plant species, but can be correlated with special ecosystemal conditions, it should be seen as a special adaptation to plant surviv al under oxygen shortage stress.