Assimilation and release of C-14 in a tropical strain of Cryptomonas obovata (Cryptophyceae) exposed to several irradiances

Carbon assimilation (C-14) and dissolved organic carbon ((DOC)-C-14) releas e by a tropical strain of Cryptomonas obovata was studied. Cells were expos ed to a range of irradiances (0-2000 mu mol m(-2) s(-1)) using axenic batch cultures in the laboratory (E-k = 180 mu mol m(-2) s(-1)). At up to 2000 m u mol m(-2) s(-1) carbon assimilation was not inhibited and an acclimation to low irradiances was observed. (DOC)-C-14 release was dependent on carbon fixation and no increase was detected under high irradiances. To determine particulate organic carbon ((POC)-C-14) loss and (DOC)-C-14 release, cells acclimated to 350 mu mol m(-2) s(-1) were incubated during 4 h at 35, 350, 850 and 1900 mu mol m(-2) s(-1). (DOC)-C-14 release was responsible for 30 % of the (POC)-C-14 loss at 1900 mu mol m(-2) s(-1). High- and low-molecula r-weight (HMW, LMW) compounds were released by C.obovata under all irradian ce conditions. However, increased release with exposure time was observed o nly for the HMW compounds.