Aquatic Sciences Meeting, Albuquerque 2001

CS41 Phytoplankton: Nutrient Dynamics and Physiology

Date: Friday, February 16, 2001, Time: 9:00:00 AM

Location: Galisteo

Tortell, P, D, Princeton University, Princeton , USA, ptortell@phoenix.princeton.edu

Morel, F, M, Princeton University, Princeton, USA, morel@princeton.edu

INORGANIC CARBON ACQUISITION BY EASTERN SUB-TROPICAL PHYTOPLANKTON ASSEMBLAGES

We report the results of recent field experiments examining the C uptake system of diverse natural assemblages both in situ and in CO2 manipulation experiments. Using the isotope disequilibrium technique, we have obtained compelling evidence for HCO3- utilization in a variety of diverse phytoplankton communities. In diatom-dominated assemblages, HCO3- is dehydrated extracellularly to CO2 (via a periplasmic carbonic anhydrase) which is subsequently transported across the plasmalemma. In contrast, algal communities dominated by cyanobacteria (Synechococcus spp.) appear to directly transport HCO3- into the cell as a substrate for photosynthesis. In two incubation experiments, we observed a CO2-dependent regulation of the C uptake system. Whereas HCO3- utilization was evident in phytoplankton assemblages grown at 150 ppm CO2, cells cultured with 800 ppm CO2 lacked external carbonic anhydrase activity and appeared to rely solely on CO2 as a source of carbon for photosynthesis. Our findings, which are consistent with previous laboratory studies of C acquisition in phytoplankton, demonstrate that HCO3- utilization is prevalent in natural phytoplankton communities and suggest that the physiological mechanisms of C transport and assimilation differ among taxa and habitats.

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Aquatic Sciences Meeting, Albuquerque 2001

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