Algal 14C and total carbon metabolisms. 2. Experimental observations with the diatom Skeletonema costatum

Abstract

Three sets of comparisons of net and gross inorganic carbon assimilation and 14C uptake were made with an axenic culture of Skeletonema costatum. The comparisons showed that in the physiological window studied (10-20% of the intrinsic generation time and gross photosynthesis/respiration ratios of 2-3), 14C uptake into the particulate plus the dissolved fractions approximated to net photosynthesis. Rate constants derived from the chemically determined changes were used to parameterize models that accounted for the respiration of photosynthetic products and for the recycling of respiratory CO2. The conclusion drawn was that over the time scale studied, the 14C technique was measuring net photosynthesis, consistent with essentially 100% recycling of respiratory CO2. The study has shown that we now possess the basis to make a rigorous analysis of net, gross CO2 fixation and net 14C uptake, and forms the first step in the development of algorithms for the interpretation of 14C field observations.