Carbon and nitrogen fluxes in the marine coccolithophore Emiliania huxleyi grown under different nitrate concentrations

  • Coccolithophores are important primary producers and the most prolific calcifiers in the ocean. Since carbon (C) and nitrogen (N) assimilation are tightly connected, N availability has a crucial impact on photosynthesis and calcification, and therefore affects the biogeochemical function of coccolithophores in the sea. In general, N availability limits primary production in many areas in the ocean. Furthermore, N availability is expected to decrease in the near future, due to increased thermal stratification in the surface ocean and reduced nutrient input from deeper waters. Keeping this in mind, we examined the effects of NO3- availability on C and N assimilation in the marine coccolithophore Emiliania huxleyi under saturating light and present day pCO2. Although growth rates and C to N ratios were similar in low and high NO3--grown cells, cellular organic C and N, and also inorganic C decreased under low NO3-. Growth at low NO3- caused a higher proportion of fixed C to be allocated to lipids relative to carbohydrates and proteins. Low NO3- availability led to downregulation of nitrate reductase (NR), nitrite reductase (NiR) and phosphoenolpyruvate carboxykinase (PEPCK) maximal activities (Vmax), up-regulation of glutamine synthetase (GS) and glutamate synthase (GOGAT) Vmax, and down-regulation of net photosynthesis and HCO3- uptake. The apparent Chl α specific efficiency of light harvesting (α) and CO2 uptake remained similar, irrespective of the NO3- concentration in the culture medium. The affinity of NR for NO3-, NiR for NO2- and GS for Glu, as well as the affinities of inorganic C uptake were higher under low NO3-. This study suggests that maintenance of a constant C to N ratio under low and high NO3- requires a concerted regulation of the intracellular CO2 and NO3- concentrations to equilibrate the fluxes through the C and N assimilation pathway.

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Publishing Institution:IRC-Library, Information Resource Center der Jacobs University Bremen
Granting Institution:Jacobs Univ.
Author:Athanasios Kaffes
Referee:Angela Koehler, Laurenz Thomsen, Silke Thoms, Bjoern Rost, Dieter Wolf-Gladrow
Advisor:Angela Koehler
Persistent Identifier (URN):urn:nbn:de:101:1-2013052411342
Document Type:PhD Thesis
Date of Successful Oral Defense:2010/01/29
Date of First Publication:2010/02/19
PhD Degree:Biology
School:SES School of Engineering and Science
Other Organisations Involved:Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung
Library of Congress Classification:G Geography. Anthropology. Recreation / GC Oceanography / GC109-149 Chemical oceanography
Call No:Thesis 2010/2

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