Modelling the interactions between ammonium and nitrate uptake in marine phytoplankton

Abstract

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.

Phytoplankton response to nutrient enrichment in an urbanized estuary: Apparent inhibition of primary production by overeutrophication

“…However, PO 4 does not appear to be limiting at stations with high NH 4 . This interesting phenomenon clearly needs further evaluation because it seemingly contradicts the advantage to phytoplankton of preference for NH 4 over NO 3 (Dortch 1990;Flynn et al 1997). We have confirmed this with a paired mesocosm study in the Delaware Estuary in which identical communities were supported by NO 3 or NH 4 and showed greater production with NO 3 (Parker 2004).…”

An optimization‐based model of iron—light—ammonium colimitation of nitrate uptake and phytoplankton growth

“…Fully dynamic approaches to carbon and nitrogen cycling have recently been proposed (Flynn et al 1997;Sciandra et al 1997;Geider et al 1998), and Flynn (pers. comm.…”

“…One important simplification is that carbon metabolism and nitrogen metabolism are treated as being independent, whereas recent empirically based model structures allow carbon acquisition to depend on cell nitrogen (Sciandra et al 1997;Geider et al 1998). Explicit modeling of physiological feedbacks between internal nitrogen stores and external ammonium and nitrate pools (Flynn et al 1997) has also been suppressed for biogeochemical clarity. Nevertheless, the model structure provides a geochemically relevant framework within which new physiological results can be interpreted; it may therefore serve as a common meeting ground among physiologists, ecosystem modelers, and geochemists.…”

A mechanistic model of photoinhibition

“…The photoinhibition model was incorporated within the ammonium-nitrate interaction model (ANIM) of Flynn et al (1997). The simple photosynthesis component in ANIM was updated to that of Flynn & Flynn (1998) (Eqn 1), and the chlorophyll synthesis term was replaced with that of Geider et al (1998) (Eqn 2).…”