Macromolecular labelling patterns and inorganic nutrient limitation of a North Atlantic spring bloom

Abstract

ABSTRACT. Synthesis rates of macromolecular classes (protein, polysaccharide, neutral lipid, glycolipid and phospholipid) were measured using 14C incorporation to assess the physiological condition of phytoplankton during a spring bloon~ in the northeastern Sargasso Sea. The relative allocation of labelled photosynthate to polysaccharide increased with incubation irradiance, and declined overnight; opposite trends were found in the protein fraction. The rate of protein synthesis at night was a small fraction (0 to 23 '%I) of the day-time rate. Incubation irradiance and overnight metabolism had relatively little effect on total or class-specific lipid synthesis. lnorganic nutrients decreased to below analytical detection during the sampling period, with coincident declines in chlorophyll a concentrations. The relative allocation of photosynthate to protein was much reduced in the nutrient-depleted stations later on in the bloom, while the allocation to polysaccharide was increased. Total lipid synthesis was only slightly higher in the later stations, but the proportion of neutral lipid was significantly increased. The changes In macrornolecular labelling patterns were consistent with a physiological response to nutrient depletion by the phytoplankton, and a reduction of 50 % or more in specific growth rates.

Biosynthesis of macromolecular and lipid classes by phytoplankton in the Northeast Water Polynya

“…Allocation to macromolecular classes was determined using a variation of the Li et al (1980) method, as previously applied in the North Atlantic (Smith & D'Souza 1993). In brief, the filters were first extracted in 2:l ch1oroform:methanol at -20°C and the extract filtered through a GF/F filter.…”

“…Allocation of photosynthate among lipid classes was determined using the method described by Smith & D'Souza (1993). In brief, chloroform lipid extracts were loaded on pre-packed silica gel columns (Sep-Pak, Waters Associates, Milford, MA, USA) and eluted with a sequence of 6 solvent phases of increasing polarity.…”

“…Nutrients and taxonomic affiliation both influence the proportion of fixed carbon that phytoplankton direct to lipids (Shifrin & Chisholm 1981, Madariaga 1992, Fernandez et al 1994a) and there has been some success in predicting lipid biosynthesis from environmental factors in freshwater phytoplankton communltles (Wainmann & Lean 1992). The total lipid pool comprises several functionally distinct classes of compound (Gurr & Harwood 1991) and previous work with natural marlne phytoplankton has shown that changing allocation to different classes underlies variations in total lipid concentration (Parrish 1987) and synthesis (Smith & D'Souza 1993). The neutral lipid class is of speclal interest as a potentially speciflc indicator of nutrient stress.…”

Primary production, calcification and macromolecular synthesis in a bloom of the coccolithophore Emiliania huxleyi in the North Sea

“…At particular stations, lipid carbon was partitioned into 3 classes (neutral lipid, polar lipids and phospholipids) by using silica gel chromatography (Smith & D'Souza 1993) as explained in Fernandez et al (1994). Radioactivity on each fraction was measured on a Packard 2500 liquid sc~ntillation counter.…”

Modeling carbon to nitrogen and carbon to chlorophyll a ratios in the ocean at low latitudes: Evaluation of the role of physiological plasticity

“…These observations exceed the values obtained in the simulations. Smith and D'Souza's (1993) observations were made at the end of the spring bloom before the microbial loop would have become well established and when nutrient stress would be expected to be particularly severe and might not apply latter in the season.…”