Exudation of organic carbon by the seagrass Halodule wrightii Aschers. And its effect on bacterial growth in the sediment

Abstract

Between 6 and 28% (mean: 14%) of 14C fixed by the leaves of Halodule wrightii Aschers, was translocated to the rhizomes and roots within 6 h. In the same time period 6 to 17% (mean: 11%) of total fixed 14C was exuded into the sediment. About 1% was excreted into the water column. Bacterial production was determined using two methods: the rate of tritiated thymidine incorporation into DNA and the rate of 32P incorporation into phospholipid. Bacterial production was 180 to 190mg C · m −2 · day −1 and was probably dependent on root decomposition as well as exudation. From the results of lipid analyses and synthesis it was concluded that bacteria were utilizing all the exuded organic 14C. Most bacterial production was in the top 20 mm of sediment, which was the zone with the greatest root and rhizome biomass. Most of the 14C exudate was also found in this zone.