Phytoplankton photosynthetic efficiency and primary production rates estimated from fast repetition rate fluorometry at coastal embayments affected by upwelling (Rías Baixas, NW of Spain)

Abstract

Previous studies have not always found a significant relationship between fast repetition rate fluorometry (FRRF)-derived and 14C-based primary production rates. This apparent discrepancy might be related to environmental control of the coupling between photosynthetic electron transport through photosystem II (PSII) and carbon uptake in phytoplankton. In this study, we looked at this relationship under upwelling conditions favourable for phytoplankton growth. The combination of both techniques allowed the calculation of the quantum efficiency of carbon fixation, which averaged 0.12 mol C (mol quanta)-1 indicating that phytoplankton populations were very efficient in converting absorbed photons into photosynthetically produced organic carbon. The tight coupling observed between phytoplankton photosynthetic electron transport through PSII and carbon uptake resulted in a statistically significant linear relationship between FRRF-derived and 14C-based carbon incorporation rates, with a slope of 1.43. In conclusion, the results of the this study indicate that FRRF can be a useful tool to derive high spatial and temporal resolution primary production estimates under environmental conditions favouring the close coupling between PSII electron transport and carbon uptake, such as those characteristic of this coastal upwelling system. © The Author 2006. Published by Oxford University Press. All rights reserved.