Quantification of track and grain density autoradiography and evaluation of 14C loss on preservation

Sources of error in quantifying autoradiography were determined with unialgal cultures and natural assemblages. Carbon-14 activity of cells as recorded by track autoradiography was generally not significantly different from scintillation counts. Differences which did occur were apparently due largely to filter-retained extracellular 14 C. An analysis of 37 preparations confirmed that tracks per cell for healthy log-phase populations followed a Poisson distribution. Quantification and analysis of intraspecific distributions for the grain density technique were relatively difficult. 14 C loss on preservation was lower and more consistent (0–21 %) than previously reported. Autoradiographs indicated that this loss consisted of unfixed filter-retained 14 C or an extracellular release product rather than carbon within algal cells. Thus, track autoradiography was more reliable for quantifying species-specific net productivity than other studies have indicated.