Gas Movements in the Roots of Avicennia marina (Forsk.) Vierh

Abstract

Apparatus for the determination of the rates of oxygen diffusion through excised portions of the root system of Avicennia marina is described. The diffusive resistances of portions of the horizontal root system are measured and the results compared with the values predicted by simple formulations of Fick's first law of diffusion. Predictions of oxygen diffusion rates made without making allowance for respiration or tortuosity are in close agreement with the measured values and thus it is concluded that the horizontal root system is a highly efficient means of oxygen transport. The diffusive resistances of a selection of pneumatophores are also measured and the effect of epiphytic algae is assessed. Structural studies of both horizontal roots and pneumatophores help to explain the ease with which gas moves within the root system, which is compared in conceptual terms with a series of open tubes.