EFFECT OF AERATION RATES ON GROWTH-RATES AND NATURAL ABUNDANCE C-13/C-12 RATIO OF PHAEODACTYLUM-TRICORNUTUM

Studies of the photosynthetic assimilation of inorganic carbon by the marine diatom Phaeodactylum tricornutum showed that the aeration system has a major influence on the dissolved inorganic carbon (DIC) concentration and hence growth rates. The stable isotope ratio of C-13/C-12 was used as an indicator of carbon limitation. Three aeration systems were used. Algae from a well-aerated culture (2 dm min-1) had a specific growth rate of 1.58 d-1, reached a cell density of 12 x 10(6) cells cm-3, displayed a constant deltaC-13 value of -23.6 parts per thousand and the inorganic carbon concentration of the growth media remained above 1.5 mol m-3. Algae from non-aerated cultures had the lowest growth rate (0.42 d-1 after 4.5 d), were able to consume DIC faster than the resupply of atmospheric CO2, and the DIC concentration reached 0.68 mol m-3 after 6.5 d of culture. The deltaC-13 value of these algae rose to -17.83 parts per thousand. Algae that were poorly aerated (0.1 dm3 min-1) had intermediate growth rates (0.72 d-1 at 4.5 d) and reduced the DIC concentration to 0.17 mol m-3 after 6.5 d. Algae grown under these conditions displayed the highest deltaC-13 values, -12.3 parts per thousand. Aeration (2 dm3 min-1) of a previously unaerated culture restored the DIC concentration of the culture medium to 2.0 mol m-3 and reduced the deltaC-13 from -14.0 parts per thousand to -23.4 parts per thousand.