Abstract
The function of the elected pneumatophores of two mangrove species, Avicennia marinaand Sonneratia alba, was investigated. Experiments were carried out with detached samples from the habitat in order to clarify that the photosynthetic reaction takes place at the surface of the pneumatophore and plays an important role in the gas exchange between the pneumatophore and the root in the subsoil.
As a result, the gross photosynthetic rates of the pneumatophores ofA. marinaandS. albawere 3 and 11 mgCO2/dm2/hr, respectively, at the light intensity of 0.45 cal/cm2/min. Their light compensating points were at 0.02-0.03 cal/cm2/min and similar to that of a shaded leaf. The diffusion rates of O2from the pneumatophores to the roots in the light condition were higher than those in the dark condition. In addition, O2diffusion rates increased when the pneumatophores were supplied with CO2through their cut surfaces.
These facts show that O2is produced by the photosynthetic reaction in the pneumatophores during daytime. Then O2diffuses to the root in the subsoil where it is used for the root respiration. In addition, the respiratory induced CO2diffuses to the pneumatophore and is used for the photosynthesis in the pneumatophore.
