Towards an understanding of species-specific differences in the photon use efficiency of diatoms

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Diatoms are an ecologically important group of algae having significant impact on global warming, because they contribute about 25% to the global primary production. The photosynthetic apparatus differs in many aspects from green plants and the physiological mechanisms which regulate the carbon assimilation in response to light and carbon limitation are still unknown. Recently, ecotypes of diatoms have been identified which differ in the kinetics and mechanisms of the photoprotective non-photochemical fluorescence quenching (NPQ) as well as in their utilization of the C3- or the C4-pathway for primary carbon fixation. However, nothing is known about the consequences of the different NPQ-mechanisms and the C3/C4 carboxylation on the photon use efficiency when the cells are grown under a dynamic light climate and suboptimal carbon availability. The understanding of the photon use efficiency under these conditions is of crucial importance for the determination of the primary production of diatoms under field conditions by bio-optical models, and in particular by means of fluorescence-based data sets. The results will clarify the quantitative importance of the different carbon assimilation pathways in diatoms and will improve the applicability of fluorescence-based models of primary production for the future.