Gas transport and storage in the Egeria densa Planch. lacunar system. Abstract

Murray-Darling Freshwater Research Centre

MDFRC item.

Egeria densa is a large aquatic angiosperm with an extensive lacunar airspace system in the shoots and roots. Oxygen produced in the chloroplasts is partitioned to both the external liquid and the lacunar system. In the light O2 entering and pressurising the lacunae diffuses to the roots down a 5% per metre concentration gradient. At the roots, some of the transported O2 sustains aerobic respiration of the tissue, and the excess is released into the sediment, oxidizing the rhizosphere. This longitudinal O2 transport is a diurnal phenomenon; corresponding diurnal fluctuations of 0.4 µgO2. cm-2. min-1 were found for the rhizosphere O2 flux.Diffusion of CO2 from roots to shoots provides an additional carbon source for photosynthesis. This results in a root-derived CO2 concentration gradient along the shoot axis.In the dark dissolved O2 around the plants may be depleted. A lower demand for external O2 by shoots with gas-filled lacunae, than by shoots with water-infiltrated lacunae, demonstrated that radial O2 diffusion in the lacunae assists nocturnal aeration of Egeria.