The Effects of Elevated Oxygen Levels on Carbon Isotopic Fractionation in the Marine Diatom Phaeodactylum tricornutum

Abstract

The carbon isotopic composition of the marine diatom Phaeodactylum tricornutum (13 C) was measured over a series of continuous culture systems with a constant growth rate () and varying O2/CO2 ratios. The 13 CCO2 and [CO2]aq were determined for each system. By comparing the fractionation (∈p) to the /CO2 it is shown that there is still a relationship between the two factors. The /CO2(aq) ranged from 0.030 to 0.163 kg mol-1 d-1 and €p ranged from 21.74 to 24.48. The results from this experiment show that high levels of O2 affect the carbon isotopic fractionation in Phaeodactylum tricornutum. It was shown that there was a variation in the 13 CCO2 with the change in O2/CO2 ratios. One likely explanation for the variation in fractionation could be due to the fixation of the 13C depleted CO2, formed during photorespiration. Further research would be required to ensure that photorespiration was the cause of the variation in 13 CCO2.