ABSTRACT
The protein labeling method provides estimates of nitrogen (N)-assimilation and relative growth rates of phytoplankton populations in the open ocean. The method was devised to circumvent some of the inherent problems associated with the N method in oligotrophic ocean waters. Donald G. Redalje analyzed seven marine species under 35 distinct N-limited conditions and found a ratio of 2.7 between the fraction of protein carbon (C) and N/C, in close agreement to the analysts' estimated value of 2.8. Various solvent fractionation schemes have been developed to separate macromolecules but all are basically derived from the early work of Roberts et al. The main advantages of the protein labeling method are: the estimated N-assimilation rates are specific for phytoplankton and the method measures total N-assimilation from all organic and inorganic N compounds, hence, a single C incubation can provide an estimate of the total autotrophic N-assimilation rate.
