Time‐course development of 14C specificactivity of chlorophyll a, carbon, and proteins in algal cultures

Abstract

The 14C labeling of Chl a, C, and protein was followed in eight algal batch cultures and three algal continuous cultures. High pressure liquid chromatography and paper chromatography were applied in purifying Chl a. From methodological investigations, we concluded that time‐course measurements of 14C specific activities for Chl a, C, and protein gave similar results as long as turnover of the inorganic C pool reduced the specific activity of inorganic C by ≲ 30%. In these cases growth rates estimated from labeling of total algal C overestimated net growth rates by ∼ 18%. Chl a C‐specific activities consistently exceeded particulate C specific activities in dense cultures when inorganic C turnover reduced the specific activity of the inorganic C by ≳ 65%. The difference in specific activity was positively correlated with the degree of isotope dilution. When the growth rates based on labeling of Chl a were corrected for isotope dilution, they exceeded growth rates estimated from changes in particulate C by ∼ 12%, the difference presumably reflecting respiratory loss of algal C. However, even when isotope dilution corrections were applied, growth rates estimated from particulate C labeling consistently underestimated net growth rates when the specific activity of the inorganic C declined by >65%. The degree of underestimation was positively correlated with the extent of isotope dilution.