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Inorganic carbon uptake and intracellular assimilation by subarctic Pacific phytoplankton assemblages
Author(s) -
Tortell Philippe D.,
Martin Cheryl L.,
Corkum Miranda E.
Publication year - 2006
Publication title -
limnology and oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 197
eISSN - 1939-5590
pISSN - 0024-3590
DOI - 10.4319/lo.2006.51.5.2102
Subject(s) - rubisco , total inorganic carbon , phosphoenolpyruvate carboxylase , phytoplankton , carbonic anhydrase , chlorophyll a , chemistry , photosynthesis , botany , biology , environmental chemistry , nutrient , carbon dioxide , biochemistry , ecology , enzyme
We report the results of inorganic carbon (C) uptake experiments and activity measurements for carbonic anhydrase, ribulose 1,5‐bisphosphate carboxylase/oxygenase (Rubisco), and phosphoenolpyruvate carboxylase (PEPC) in offshore and coastal regions of the eastern subarctic Pacific Ocean. HCO 3 ‐ was the dominant source of inorganic C taken up by phytoplankton at all sampling locations, accounting for ∼60−90% of total C uptake. The uptake of HCO 3 ‐ occurred primarily through a direct transport system, while indirect HCO 3 − use, mediated by extracellular carbonic anhydrase (eCA), played a minor role in the C uptake system. Direct HCO 3 ‐ transport and eCA activity were not related to ambient nutrient or CO 2 concentrations or to phytoplankton biomass (chlorophyll a [Chl a ]) or primary productivity. There was significant variability in the biomass‐normalized activities of Rubisco, PEPC, and total (intracellular and extracellular) carbonic anhydrase. The activities of all of the enzymes measured exhibited significant correlations with both CO 2 concentrations and Chl a . PEPC activity averaged 20% of Rubisco activity (range 0.5‐110%), and the PEPC : Rubisco ratio was positively correlated with CO 2 concentrations and negatively correlated with Chl a . Carbonic anhydrase activity was strongly anticorrelated with CO 2 and positively correlated with Chl a . The results provide evidence for the importance of CO 2 ‐regulated carbon concentrating mechanisms in marine waters.