Rapid incorporation of 13N03 by NH4- limited phytoplankton

Zehr, Jonathan P.; Capone, D G; Falkowski, P. G.

doi:10.3354/meps051237

Cited by 14 publications

(10 citation statements)

References 16 publications

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“…with respect to the structure of the model and its performance. Events such as the simultaneous transport and assimilation of nitrate and ammonium (Zevenboom & Mur 1981;Quegumer et al 1986;Zehr et al 1989) may be readily accounted for. Although not an aim of the model, the simulation of the responses of the GLN pool to N starvation and refeeding with nitrate or ammonium is realistic on a quantitative and temporal basis (e.g.…”

Section: Discussionmentioning

confidence: 99%

Modelling the interactions between ammonium and nitrate uptake in marine phytoplankton

Flynn

Fasham

Hipkin

1997

Phil. Trans. R. Soc. Lond. B

132

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CONTENTS page 1. Introduction 1625 2. Theoretical bases and model development 1626 (a) Model construction 1626 (b) Control of transport (figures 2, 3; equation 5.x in table 5) 1629 (c) Nitrate reduction to ammonium (figures 2, 3; equation 6.x in table 6) 1630 (d) Assimilation of intracellular ammonium and growth (figures 2, 3; equation 7.x in table 7) 1633 (e) Operation in light-dark cycles 1635 (f) Parametrization 1635 3. Results 1635 (a) Simulation of ammonium-nitrate interactions 1635 (b) Sensitivity analysis 1637 4. Discussion 1639 References 1643 SUMMARY An empirically based mathematical model is presented which can simulate the major features of the interactions between ammonium and nitrate transport and assimilation in phytoplankton. The model (ammonium-nitrate interaction model), which is configured to simulate a generic microalga rather than a specified species, is constructed on simplified biochemical bases. A major requirement for parametrization is that the N:C ratio of the algae must be known and that transport and internal pool sizes need to be expressed per unit of cell C. The model uses the size of an internal pool of an early organic product of N assimilation (glutamine) to regulate rapid responses in ammoniumnitrate interactions. The synthesis of enzymes for the reduction of nitrate through to ammonium is induced by the size of the internal nitrate pool and repressed by the size of the glutamine pool. The assimilation of intracellular ammonium (into glutamine) is considered to be a constitutive process subjected to regulation by the size of the glutamine pool. Longer term responses have been linked to the nutrient history of the cell using the N:C cell quota. N assimilation in darkness is made a function of the amount of surplus C present and thus only occurs at low values of N:C. The model can simulate both qualitative and quantitative temporal shifts in the ammonium-nitrate interaction, while inclusion of a derivation of the standard quota model enables a concurrent simulation of cell growth and changes in nutrient status.

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Section: Discussionmentioning

confidence: 99%

Modelling the interactions between ammonium and nitrate uptake in marine phytoplankton

Flynn

Fasham

Hipkin

1997

Phil. Trans. R. Soc. Lond. B

132

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“…However, in the present case, nitrate uptake was correlated in a highly significant manner to chl a and the Y‐intercept was not different from zero, indicating negligible bacterial uptake of nitrate. Those high values were also criticized by Zehr et al (1989), who partially attributed them to artificial stimulation by isotope addition. Although this may be true for ammonium, it cannot be the case for nitrate given the initial concentrations (20.1–49.1 μmol N·L −1 ) and isotope addition (2.9 μmolN· L −1 ) that represented a substrate increase of only 6%–14% above ambient levels.…”

Section: Upwelling Areasmentioning

confidence: 99%

ACCLIMATION OF NITRATE UPTAKE BY PHYTOPLANKTON TO HIGH SUBSTRATE LEVELS¹

Collos

Vaquer

Souchu

2005

Journal of Phycology

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A literature review of data on nitrate uptake by phytoplankton suggests that nitrate levels above 20 lmol N . L À 1 generally stimulated uptake rates in cultured unicellular algae and natural phytoplankton communities. This phenomenon indicates that phytoplankton cells acclimate to elevated nitrate levels by increasing their uptake capacity in a range of concentrations previously considered to be saturating. Cyanobacteria and flagellates were found to present a considerable capacity for acclimation, with low (0.1-2 lmol N . L À 1 ) half-saturation values (K s ) at low (5-20 lmol N . L À 1 ) substrate levels and high (1-80 lmol N . L À 1 ) K s values at high (30-100 lmol N . L À 1 ) substrate levels. However, some diatom genera (Rhizosolenia, Skeletonema, Thalassiosira) also appeared to possess a low affinity nitrate uptake system (K s between 18 and 120 lmol N . L À 1 ), which can help resolve the paradox of their presence in enriched seas. It follows that present models of nitrate uptake can severely underestimate the effects of high nitrate concentrations on phytoplankton dynamics and development. A more adequate approach would be to consider the possibility of multiphasic uptake involving several phase transitions as nitrate concentrations increased. Because it is a nonlinear phenomenon featuring strong thresholds, this effect appears to override that of other variables, such as irradiance, temperature, and cell size. Within the present context of eutrophication and for a range of concentrations that is becoming more and more ecologically relevant, equations are tentatively presented as a first approach to estimate K s from ambient nitrate concentrations.

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“…For example, Collos (1980) showed a great decline of uptake rates measured over 1 h after 24 h starvation when initial nitrate concentrations were high (5 to 20 PM), but at a concentration lower than 1 pM there was no significant difference from non-deficient cells. In the same way, using small additions (4100 nM) of labelled nitrate (I3N), Zehr et al (1989) reported a rapid absorption of nitrate and its incorporation into protein in ammonium-limited cells due to the activity of the constitutive nitrate reductase. A better understanding of nitrate uptake by marine phytoplankton is needed to determine how N-depleted phytoplankton respond and adapt to episodic nitrate supplies occurring at nanomolar levels in the field.…”

Section: Introductionmentioning

confidence: 80%

Short-term responses of 24 hour N-starved cultures of Phaeodactylum tricornutum to pulsed additions of nitrate at nanomolar levels

Raimbault¹,

Gentilhomme²,

Slawyk³

1990

Mar. Ecol. Prog. Ser.

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A high cell-density chemostat culture and a dilute sample, obtained by adding chemostat culture to a nitrate-free medium, were used to study the uptake of low nitrate concentrations by 24 h nitrogen-starved populations of the diatom Phaeodactylum tricornutum Bohlin. In contrast with numerous previous studies, nitrate was immediately taken up at a high rate following pulsed nitrate additions of 15 to 100 nM. These initial rates exceeded the daily growth rate (0.046 h-") by a factor of 2 5 over a short time during which the population took up 65 to 80 % of the nitrate added. In high cell-density cultures the transient uptake rate rapidly declined due to the rapid decrease of ambient nitrate, while in dilute cultures high uptake rates were sustained for more than 1 h. Although starvation greatly changed the pattern of the nitrate pulse utilization, this diatom appears to be able to meet its nitrogen requirements in response to a sudden increase of nitrate in the nanomolar range.

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Rapid incorporation of 13N03 by NH4- limited phytoplankton

Cited by 14 publications

References 16 publications

Modelling the interactions between ammonium and nitrate uptake in marine phytoplankton

Modelling the interactions between ammonium and nitrate uptake in marine phytoplankton

ACCLIMATION OF NITRATE UPTAKE BY PHYTOPLANKTON TO HIGH SUBSTRATE LEVELS¹

Short-term responses of 24 hour N-starved cultures of Phaeodactylum tricornutum to pulsed additions of nitrate at nanomolar levels

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Rapid incorporation of 13N03 by NH4- limited phytoplankton

Cited by 14 publications

References 16 publications

Modelling the interactions between ammonium and nitrate uptake in marine phytoplankton

Modelling the interactions between ammonium and nitrate uptake in marine phytoplankton

ACCLIMATION OF NITRATE UPTAKE BY PHYTOPLANKTON TO HIGH SUBSTRATE LEVELS1

Short-term responses of 24 hour N-starved cultures of Phaeodactylum tricornutum to pulsed additions of nitrate at nanomolar levels

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ACCLIMATION OF NITRATE UPTAKE BY PHYTOPLANKTON TO HIGH SUBSTRATE LEVELS¹