TRANSPORT OF CARBON AND EXCRETION OF DISSOLVED ORGANIC-CARBON BY L LEAVES AND ROOTS RHIZOMES IN SEAGRASSES AND THEIR EPIPHYTES

Transport of carbon between the rooting organs and foliage and the extracellular release of dissolved organic carbon (DOC) was examined experimentally in three species of seagrass. Carbon taken up by roots/rhizomes was transported to the leaves and to water surrounding the leaves. Carbon fixation in leaves was small in Zostera marina L. and Thalassia testudinum Banks et König (5-20% of C taken up by roots) but nearly equal to that incorporated in the roots in Halodule wrightii Aschers. A greater percentage of carbon transported from the roots accumulated in the leaves and epiphytes of Halodule than in the other two species. Altering the oxygen concentrations of water surrounding the roots/rhizomes had only minor effects on the uptake and transport of carbon from either the roots or the leaves. Excretion of DOC as a percentage of carbon fixed was low but was consistently lower from Halodulel than from Zostera or Thalassia. Generally, over 50% of the excreted DOC was of a molecular weight >10,000 Daltons. Low molecular weight (<500 Daltons) excreted DOC was less than 30% of the total and decreased in the presence of epiphytes. © 1979.