Extracellular products of photosynthesis in a tropical environment

Abstract

Extracellular products in the Arabian Sea averaged 0.42 g/cm2/day and represented 35% of the total carbon fixed by phytoplankton. No seasonal changes are observed during the two seasons i.e. premonsoon (Jan-Feb) and onset of southwest monsoon (April - May). Maximum extracellular production occurred at the surface in contrast to the sub-surface maxima in particulate production. Percentage extracellular release was higher (35%) in the nutrient limited waters of the Arabian Sea as compared to only 7.6% in the estuarine waters of Dona Paula, Goa, where nutrients are seldom limiting. A partially modified radiochromatographic method was used to identify some of the photosynthetic products released. Glycollic acid, a product of photorespiration and one of the more commonly occurring products of excretion did not appear to be a major excretory compound. It constituted only 2-32% of the total radioactivity and was present in only 34% of the samples. Citrate was tentatively identified as another product of extracellular release. Unidentified acids comprised 2-78% of the total radioactive material recovered from the phytoplankton exudate