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

Abstract

Carbon assimilation (14C) and dissolved organic carbon (DO14C) release by a tropical strain of Cryptomonas obovata was studied. Cells were exposed to a range of irradiances (0-2000 μmol m-2 s-1) using axenic batch cultures in the laboratory (E(k) = 180 μmol m-2 s-1). At up to 2000 μmol m-2 s-1, carbon assimilation was not inhibited and an acclimation to low irradiances was observed. DO14C release was dependent on carbon fixation and no increase was detected under high irradiances. To determine particulate organic carbon (PO14C) loss and DO14C release, cells acclimated to 350 μmol m-2 s-1 were incubated during 4 h at 35, 350, 850 and 1900 μmol m-2 s-1. DO14C release was responsible for 30% of the PO14C loss at 1900 μmol m-2 s-1. High- and low-molecular-weight (HMW, LMW) compounds were released by C. obovata under all irradiance conditions. However, increased release with exposure time was observed only for the HMW compounds.