Optimal uptake kinetics: physiological acclimation explains the pattern of nitrate uptake by phytoplankton in the ocean.

Smith, S. Lan, Yamanaka, Yasuhiro, Pahlow, Markus and Oschlies, Andreas (2009) Optimal uptake kinetics: physiological acclimation explains the pattern of nitrate uptake by phytoplankton in the ocean. Open Access Marine Ecology Progress Series, 384 . pp. 1-12. DOI 10.3354/meps08022.

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Phytoplankton supply the base of the marine food web and drive the biogeochemical cycles of carbon and nutrients. Over much of the ocean, their growth is limited by their uptake of nitrogen (as nitrate), which has most commonly been described by the hyperbolic Michaelis-Menten (MM) equation. However, the lack of a theory to explain variations in MM constants has hindered our ability to predict the response of marine ecosystems to changes in environmental conditions. The MM equation fits data from short-term experiments well, but does not agree with steady-state experiments over wide ranges of nutrient concentrations. In contrast, the recently developed optimal uptake kinetics (OU) does agree with the latter and can also describe the observed pattern of MM half-saturation constants from field. experiments. OU kinetics explains the observed pattern of N uptake as the result of a general physiological trade-off between nutrient uptake capacity and affinity. The existence of a general trade-off would imply a relatively high degree of predictability in the response of nutrient uptake to changing nutrient concentrations and thus provide a basis for predicting effects of climate change on marine ecosystems and biogeochemical cycles.

Document Type: Article
Additional Information: Despite the lack of any firm theoretical basis for its application, the Michaelis-Menten (MM) equation has remained the basis for modeling nutrient uptake by phytoplankton (and other organisms) for decades. Typically applied using a fixed half-saturation constant, the MM equation effectively assumes a fixed physiology for nutrient uptake, with no acclimation in response to changing nutrient concentrations. Optimal Uptake (OU) kinetics allows for such acclimation and agrees with results from laboratory experiments that MM kinetics fails to describe. In agreement with observations covering broad areas of the ocean, OU predicts that half-saturation concentration should increase as the square root of nutrient concentration, and thus improves the representation of biological production in global ocean models. Inter-Research Science Publisher is pleased to make this Feature Article openly available for viewing by our readers
Keywords: Nutrient uptake; Kinetics; Phytoplankton; Nitrogen; Nitrate; Biogeochemical model
Research affiliation: OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-BM Biogeochemical Modeling
OceanRep > The Future Ocean - Cluster of Excellence
Refereed: Yes
Open Access Journal?: No
DOI etc.: 10.3354/meps08022
ISSN: 0171-8630
Projects: Future Ocean
Date Deposited: 08 Jun 2009 14:57
Last Modified: 01 Jun 2018 09:22
URI: http://oceanrep.geomar.de/id/eprint/6669

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