Light utilization and photosynthetic efficiency of Nannochloris sp. (Chlorophyceae) approached by spectral absorption characteristics and Fast Repetition Rate Fluorometry (FRRF)

The photosynthetic performance of Nannochloris sp. (Chlorophyceae) batch cultures, grown in 16:8 h light:dark cycle, was evaluated with 14C-incorporation, O2-evolution, light absorption of PSII, and variable fluorescence. Cell pigmentation, elemental composition, and photosynthetic parameters were measured in the course of one light period from cultures acclimated to 314 and 39 umol quanta m–2 s–1. Both cultures had a biphasic trend during the light period. The productivity increased during the first half of the light period, and decreased afterwards. The growth rates in both of the cultures were mainly regulated by the internal cell cycle, rather than by light and nutrients. The nutrient metabolism obviously caused discrepancy between the 14C-based and variable fluorescence-based primary productivity estimates. The relatively higher estimate of the rate of electron transport through PSII than of the 14C-based biomass-specific primary productivity in the early phases of the experiment was mainly caused by the inability of the variable fluorescence method to take into account a partial loss of ATP, NADPH and ferredoxin pools caused by the active NO3-N uptake and reduction. The temporal patterns of the fluorescence-based ([phi]f) and the 14C-based quantum yield for carbon fixation were much alike, since in the definition of [phi]f processes other than carboxylation, consuming the reducing power and the chemical energy produced by the light reaction of photosynthesis, were taken into consideration. The problems associated with the inclusion of pre-set parameters in the productivity models are also discussed.