Diel photosynthetic production of cellular organic matter in natural phytoplankton populations,measured with13C and gas chromatography/mass spectrometry

Diel photosynthetic production of water-extractable and residual carbohydrates in natural phytoplankton populations was investigated by analyzing monosaccharide components with combined gas chromatography/mass spectrometry (GC/MS) and¹³C tracer methods. The applicability of this technique for measuring the photosynthetic production of natural phytoplankton populations was examined. Phytoplankton was collected in August 1984 from Kinu-ura Bay, Japan, and incubated under natural light and dark conditions for 24 h. Cell density and concentration of chlorophylla increased about four- and three-fold, respectively, during the experimental period. Production of glucose, galactose, mannose, rhamnose, ribose, fucose, xylose and arabinose was measured in the water-extractable and residual carbohydrate fractions of the phytoplankton. Most of the monosaccharides in both fractions were produced the monosaccharides in both fractions were produced mainly during the daytime. Glucose was a major component in the water-extractable carbohydrate fraction produced by the phytoplankton, and decreased markedly at night. Thus, most of the glucose in the water-extractable carbohydrates seemed to be a constituent of the storage glucan of algal cells. Most monosaccharide components of the water-extractable carbohydrate fraction except glucose did not decrease significantly at night. Ribose of the water-extractable carbohydrate fraction was synthesized at a maximum rate in the morning, prior to the other monosaccharide constituents of this fraction. The major monosaccharide constituent in the residual carbohydrate fraction produced by the phytoplankton was glucose, which decreased significantly at night. Diel change in the production of monosaccharide constituents in residual carbohydrates indicated wide variability in the monosaccharide composition of cell-wall material in algae. The ratios of production of water-extractable and residual carbohydrates to POC production ranged from 8.8 to 28% and from 3.7 to 5.9%, respectively, throughout the daytime and nighttime.