Needoba, J. A. Department of Botany, University of British Columbia, needoba@unixg.ubc.ca
Harrison, P. A. Department of Botany, University of British Columbia, pharrisn@unixg.ubc.ca

 
INFLUENCE OF IRRADIANCE AND CELL SIZE ON NITROGEN ISOTOPE FRACTIONATION BY TWO DIATOMS GROWN ON NITRATE
 
Isotope fractionation of the stable isotopes of nitrogen was determined for two different sized diatoms during growth on nitrate under high and low irradiance. Growth rate, nitrogen concentration in the medium, and internal nitrate pools within the cells were measured. Isotope fractionation was determined from the 15N/14N ratio in the phytoplankton cells. The amount of fractionation under different light conditions depended on cell size. The small diatom Thalassiosira pseudonana shows a discrimination of 5-6 in both high and the low irradiance cultures. In contrast, the nitrogen discrimination for the large diatom Thalassiosira weissflogii dramatically increased from 6 at high light to 19 at low light. The importance of cell size and nitrate concentration within the cell will be addressed in order to explain the changes in fractionation that occur when cells are grown in low light conditions. These findings provide new insight to the physiological mechanism of nitrate fractionation in phytoplankton and will increase our understanding of nitrogen isotope fractionation in an oceanographic context.
 
Day: Tuesday, Feb. 2
Time: 08:45 - 09:00am
Location: Eldorado Hotel
 
Code: SS32TU0845E