A theoretical model for nutrient uptake in phytoplankton

Aksnes, DL; Egge, JK

doi:10.3354/meps070065

Cited by 276 publications

(322 citation statements)

References 21 publications

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“…Furthermore, there is indication from phytoplankton organisms that the maximum growth rate and the half‐saturation constant are often positively correlated (Edwards, Klausmeier, & Litchman, 2013; Litchman, Edwards, & Klausmeier, 2015). Thus, Aksnes and Egge (1991) and Smith et al. (2014) suggested an alternative mechanistic formulation of nutrient‐uptake kinetics for phytoplankton organisms which accounted implicitly for this correlation.…”

Section: Discussionmentioning

confidence: 90%

Not attackable or not crackable—How pre‐ and post‐attack defenses with different competition costs affect prey coexistence and population dynamics

Ehrlich

Gaedke

2018

Ecology and Evolution

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It is well‐known that prey species often face trade‐offs between defense against predation and competitiveness, enabling predator‐mediated coexistence. However, we lack an understanding of how the large variety of different defense traits with different competition costs affects coexistence and population dynamics. Our study focusses on two general defense mechanisms, that is, pre‐attack (e.g., camouflage) and post‐attack defenses (e.g., weaponry) that act at different phases of the predator—prey interaction. We consider a food web model with one predator, two prey types and one resource. One prey type is undefended, while the other one is pre‐ or post‐attack defended paying costs either by a higher half‐saturation constant for resource uptake or a lower maximum growth rate. We show that post‐attack defenses promote prey coexistence and stabilize the population dynamics more strongly than pre‐attack defenses by interfering with the predator's functional response: Because the predator spends time handling “noncrackable” prey, the undefended prey is indirectly facilitated. A high half‐saturation constant as defense costs promotes coexistence more and stabilizes the dynamics less than a low maximum growth rate. The former imposes high costs at low resource concentrations but allows for temporally high growth rates at predator‐induced resource peaks preventing the extinction of the defended prey. We evaluate the effects of the different defense mechanisms and costs on coexistence under different enrichment levels in order to vary the importance of bottom‐up and top‐down control of the prey community.

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Section: Discussionmentioning

confidence: 90%

Not attackable or not crackable—How pre‐ and post‐attack defenses with different competition costs affect prey coexistence and population dynamics

Ehrlich

Gaedke

2018

Ecology and Evolution

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“…First, the entire cellular surface must be receptive for nutrient absorption. Second, the absorption of one nutrient molecule cannot be hampered by the handling of a previous collision (sensu Aksnes and Egge, 1991). Such handling constraints is not reflected in the affinity coefficient and is not further elaborated in the present study.…”

Section: Introductionmentioning

confidence: 96%

Scaling Laws in Phytoplankton Nutrient Uptake Affinity

et al. 2016

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Nutrient uptake affinity affects the competitive ability of microbial organisms at low nutrient concentrations. From the theory of diffusion limitation it follows that uptake affinity scales linearly with the cell radius. This is in conflict with some observations suggesting that uptake affinity scales to a quantity that is closer to the square of the radius, i.e., to cell surface area. We show that this apparent conflict can be resolved by nutrient uptake theory. Pure diffusion limitation assumes that the cell is a perfect sink which means that it is able to absorb all encountered nutrients instantaneously. Here, we provide empirical evidence that the perfect sink strategy is not common in phytoplankton. Although, small cells are indeed favored by a large surface to volume ratio, we show that they are punished by higher relative investment cost in order to fully benefit from the larger surface to volume ratio. We show that there are two reasons for this. First, because the small cells need a higher transporter density (p) in order to maximize their affinity, and second because the relative cost of a transporter is higher for a small than for a large cell. We suggest, that this might explain why observed uptake affinities do not scale linearly with the cell radius.

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“…I hypothesize that cell size is this other factor. Half-saturation constants for nutrient uptake should increase with algal size due to surface-volume considerations (Hudson and Morel 1990), and there is theoretical (Hudson and Morel 1990;Aksnes and Egge 1991) and empirical (Eppley et al 1969;Moloney and Field 1991) evidence that this scaling should be allometric (power law). For ammonium, the allometric dependence of the half-saturation constant K on size can be written…”

Section: Origin Of the Wheeler-kokkinakis Patternmentioning

confidence: 99%

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

Armstrong

1999

Limnology & Oceanography

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The ability to model ''new'' (nitrate-based) production is crucial to predicting the ocean's role in the global carbon cycle. The ability to model the distribution of high-nutrient/low-chlorophyll (HNLC) areas is particularly important in this regard. Here I draw together three elements that appear to be necessary for constructing the required model: (1) iron limitation of algal growth rates as an ultimate cause of the HNLC condition; (2) ammonium inhibition of nitrate uptake and utilization as a proximate mechanism that leads to reduced nitrate use; and (3) the dependence of both processes on algal cell size. In the model, cells are postulated to maximize their growth rates by partitioning scarce iron between nitrogen-and carbon-related demands. The effect of iron limitation is postulated to depend on cell size through surface/volume effects on uptake efficiency; this dependence on cell size in turn affects phytoplankton community structure and community-level uptake of nitrate. The efficacy of the model is demonstrated by its ability to reproduce community-level curves of nitrate uptake versus ammonium concentration from both HNLC and non-HNLC areas. The partition formalism can be incorporated directly into ecosystem models; when implemented in an ecosystem model with multiple size classes, the model should produce HNLC versus non-HNLC conditions in appropriate locations and for appropriate reasons. In particular, the model's ability to produce iron-light and iron-light-nitrogen colimitation should be useful in understanding and predicting the HNLC condition in parts of the Southern Ocean. With suitable changes to parameter values, the postulated mechanism for iron partitioning may also prove useful in modeling iron and energy partitioning in nitrogen fixers. The ability to model the distribution of high-nutrient/lowchlorophyll (HNLC) areas, where concentrations of nitrate and phosphate remain high throughout the year, is critical to prognostic studies of the global carbon cycle. Empirical evidence suggests that the ability to model iron limitation of growth and nitrate uptake will be a key element in predicting HNLC conditions. As the prime example, a scarcity of iron has recently been shown to limit phytoplankton growth, biomass accumulation, and size and taxonomic structure in the equatorial Pacific, a major HNLC region (Coale et al. 1996). Addition of iron to surface waters of this region caused a massive phytoplankton bloom and drawdown of nitrate, accompanied by a marked reduction in the fugacity of CO 2 (Cooper et al. 1996). The possibility of similar conversion of the subarctic Pacific (La Roche et al. 1996) and the Southern Ocean (de Baar et al. 1995;Kumar et al. 1995) from HNLC to non-HNLC by the addition of iron is supported by more indirect evidence. AcknowledgmentsConversations with Richard Geider helped greatly in the development of these ideas, particularly in the realization that it could be extremely useful scientifically to have a single model of iron limitation that both biogeochem...

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A theoretical model for nutrient uptake in phytoplankton

Cited by 276 publications

References 21 publications

Not attackable or not crackable—How pre‐ and post‐attack defenses with different competition costs affect prey coexistence and population dynamics

Not attackable or not crackable—How pre‐ and post‐attack defenses with different competition costs affect prey coexistence and population dynamics

Scaling Laws in Phytoplankton Nutrient Uptake Affinity

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

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