The effect of environmental variables on release of extracellular organic carbon by freshwater macrophytes

Abstract

The14C-technique was used to investigate the effect of oxygen, inorganic carbon and light intensity on the release of extracellular organic carbon (EOC) by three submerged macrophytes. At low CO2 availability and low light intensities the release expressed as a percentage of the total carbon fixation was higher than at more optimal photosynthetic conditions. Oxygen did not influence the release of EOC. As the rates of release generally followed the rates of photosynthesis, it was concluded that release is closely coupled to photosynthesis. Using gel-filtration to separate EOC it was shown that the tested environmental variables did not influence the molecular weight distribution. The release of EOC was low in all species (0.1 to 4% of the total carbon fixation). Due to the low values it is suggested that release of EOC is of no quantitative importance to the carbon budget of the plants.