Root Aeration and Respiration in Young Mangrove Plants (Avicennia marina(Forsk.) Vierh.)

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Abstract
The roots of young plants of Avicennia marina (Forsk.) Vierh. grown under simulated tidal conditions were harvested so as to obtain the entire root system. The roots were subdivided and weighed and subsamples taken for manometric determination of respiration rates at different temperatures. The supply capacity of the above-ground portion of the root system was determined and the results compared in terms of supply and demand. The oxygen consumption rate of the roots at 15°C was found to be 1·69±0·07 μmol kg−1 s−1 for cable roots and 3·27±0·12 μmol kg−1 s−1 for fine roots. The Q10 for respiration was 2·55 for oxygen consumption in both fine and cable roots, and for carbon dioxide production was 2·66 for fine roots and 3·04 for cable roots. The respiratory quotient varied with temperature but was less than unity. Concentration differences of between 1·8 mol m−3 and 3·4 mol m−3 between the inside of root and the air were sufficient to permit aeration of the root system by diffusion alone, and the aerenchyma contained sufficient oxygen to maintain aerobic conditions while the roots were covered with water. The effect of tide and seasonal temperature change on gas exchange, together with the possibility of some form of carbon dioxide fixation within the root, are examined and the implications of these effects on growth and development are discussed.

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