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Marine Ecology Progress Series

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MEPS 376:69-83 (2009)  -  DOI:

Chain model of phytoplankton P, N and light colimitation

Markus Pahlow*, Andreas Oschlies

IFM-GEOMAR, Düsternbrooker Weg 20, 24105 Kiel, Germany

ABSTRACT: Models of multiple potentially limiting nutrients currently employ either multiplicative or threshold formulations, neither of which has a sound mechanistic explanation. Despite experimental evidence that lack of P severely constrains N assimilation, this mechanism has not been considered for constructing models of multi-nutrient limitation. We construct a phytoplankton optimal growth model linking C, chlorophyll (Chl), N, and P through a limitation chain in which P limits N assimilation, N limits photosynthesis and photosynthesis limits growth. The resulting formulation possesses characteristics of both multiplicative and threshold approaches and provides a mechanistic foundation for modelling multi-nutrient and light limitation of phytoplankton growth. The model compares well with experimental observations for a variety of unicellular phytoplankton species. It is suggested that the widely held view that N and P limitation act independently of each other is based on an invalid interpretation of experimental observations and that the transition from N to P limitation occurs over a wide range of colimitation rather than a sharply-defined transition point. If the species considered in this study are representative for marine phytoplankton, our model results indicate that most phytoplankton are colimited by N and P when inorganic N and P are simultaneously exhausted in the surface ocean. The model suggests that the close match between marine inorganic (Redfield) and phytoplankton N:P ratios results from optimal nutrient utilisation but does not indicate optimality of Redfield N:P.

KEY WORDS: N · P · Light colimitation · Redfield C:N:P · Chlorophyll dynamics

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Cite this article as: Pahlow M, Oschlies A (2009) Chain model of phytoplankton P, N and light colimitation. Mar Ecol Prog Ser 376:69-83.

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