Nitrogen storage and use of biochemical indices to assess nitrogen deficiency and growth rate in natural plankton populations

Abstract

Various newly developed indicators of N deficiency, physiological state (approximate growth rate), and N source for growth were measured during five cruises to Dabob Bay, Washington from early spring to summer. Although nitrate and ammonium in the surface layer were depleted early in the spring, the plankton populations never became extremely N deficient, as indicated by high intracellular amino acid/protein ratios. However, growth rates, estimated from protein/DNA or RNA/DNA ratios, were usually low unless nitrate concentrations were high or had recently been high, as indicated by large intracellular nitrate pools or high nitrate reductase activities. High growth rates were observed during the spring bloom or as a result of the sporadic supply of nitrate to the euphotic zone, which was inferred from measurements of biochemical indicators on several cruises after the spring bloom. The sporadic supply of nitrate could account for the lack of N deficiency in these populations and mask diel periodicity in N utilization. These results demonstrate that biochemical indicators can be easily measured in the field and that variations in indicators such as intracellular amino acid/protein, protein/DNA, RNA/DNA ratios, NR activities and intracellular nitrate concentrations are an aid in understanding plankton dynamics.

Quantifiying external and internal nitrogen and phosphorus pools, as well as nitrogen and phosphorus supplied through remineralization, in coastal marine plankton by means of a dilution technique

“…per cell or per unit carbon, may vary several-fold in response to nutrient depletion (Harrison et al 1977, Sakshaug et al 1984), testifying to their ability to grow on internal reserves. In nutrient-sufficient natural plankton, excess N or P has been shown to be present in the form of readily utilizable compounds such as amino acids (Dortch et al 1985) and orthophosphate ). According to the latter authors, orthophosphate can be stored in diatom plankton in inshore waters in quantities of up to ca 40 % of total P, so that complete utilization of this resource alone may suffice for a ca 70 % increase in biomass.…”

Intracellular NH4 and NO5 pools associated with deposited phytoplankton in a marine sediment (Aarhus Bight, Denmark)

“…Raimbault & Mingazzini 1987. and Dortch et al (1985) measured high in situ concentrations of intracellular NO; in natural assemblages of phytoplankton during a spring bloom. As for NH:, we shall therefore refer to an intracellularNO.7 pool in the sediment.…”

“…Both monocultures and naturally occurring phytoplankton populations of marine microalgae have been shown to contain intracellular pools of NH: and NOB (Dortch et al 1985 and references therein). For instance, pelagic diatoms such as Skeletonema costatum which often dominate the spring blooms of primary production in temperate coastal waters may internally contain considerable amounts of inorganic nitrogen (e.g.…”

Modified assay procedure for enhanced sensitivity of in vitro glutamine synthetase (GS) activity measurements in marine phytoplankton

“…The error bars for the individual data points in the figure also indicate the good precision obtained with the malachite green/ whole cell homogenate procedure. Application of the procedure to field samples of phytoplankton Dortch et al (1985) report efforts to measure GS activities in field samples of natural phytoplankton from Dabob Bay, Washngton (USA). Activities were not detected in samples using the original method of Bressler & Ahmed (1984) due to the relative 'insensitivity' of the assay.…”

“…The error bars included with the GS data in the figure again indicate the good precision obtained with the malachite green/ whole cell homogenate procedure. Although a more detailed presentation and discussion of this data is presented elsewhere (Dortch et al 1985), the figure does illustrate a coupling between measured in vitro activity levels for the enzyme and accompanying biomass indicators (i.e. PN and chlorophyll a).…”