CARBON ACQUISITION AND PHOTOPHYSIOLOGY OF THE MARINE DINOFLAGELLATE KARENIA BREVIS UNDER A RANGE OF CO2 CONCENTRATIONS
Karenia brevis, a bloom forming dinoflagellate, frequently forms red tides in the Gulf of Mexico. Despite its ecological and economical importance, surprisingly little is known about how this organism assimilates inorganic carbon, how it copes with reduced CO2 concentrations during dense blooms or how it might respond to an increase in atmospheric CO2. The response to CO2 is particularly interesting as the dinoflagellate Rubisco has one of the lowest K1/2 values among eukaryotic phytoplankton. K. brevis was grown in dilute batch cultures under 120, 400 and 760ppm CO2. No significant change in growth rate was detected between CO2 conditions. A distinct diurnal rhythm in photosynthesis and respiration was observed with small differences between the CO2 treatments. Generally high respiration was present during the day. Carbon fixation vs. carbon substrate kinetic measurements showed moderate affinities to inorganic carbon under all CO2 concentrations tested. HCO3- was determined to be the dominant carbon source, yet CO2 was taken up as well. The HCO3- / CO2 uptake ratio did not change significantly under different CO2 concentrations. Membrane inlet mass spectrometry measurements revealed only little external CA activity, with no clear difference between treatments. Our data is the first experimental analysis on carbon acquisition in this important dinoflagellate and shows that Karenia employs an efficient CCM to saturate RubisCO to effectively grow under any of the tested CO2 concentration. We also showed that K. brevis might not be affected by enhanced CO2 availability as projected for a future ocean.
Kranz, S. A., Florida State University, USA, firstname.lastname@example.org
Bercel, T., Florida State University, USA, email@example.com
Location: 323 B
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