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Sezginer, Yayla

University of British Columbia

Through photosynthesis, phytoplankton form the base of marine food webs and drive atmospheric CO₂ uptake through the marine biological carbon pump. Monitoring phytoplankton photosynthetic responses to changing environmental conditions is thus critical to predicting ecosystem feedbacks to climate change. Fast Repetition Rate fluorometry (FRRF) offers rapid measurements of phytoplankton photo-physiology and photosynthetic electron transport rates (ETR), which represent the ultimate source of metabolic energy for carbon fixation. This thesis aims to address several physiological and methodological considerations that presently limit the widespread use of FRRF for high resolution in-situ measurements of phytoplankton ETR. These challenges include diverging approaches to calculate ETR (Chapter 2), the influence of pre-measurement sample handling practices and variable photo-acclimation states on ETR measurements (Chapter 3), and variability in the stoichiometry between ETR and downstream carbon fixation (Chapter 4). The field-based studies presented in this work illustrate how natural light and nutrient gradients influence photo-physiology, FRRF signatures and their interpretation. Results presented in Chapter 2 reveal that the coherence between ETR estimates derived from different algorithms varies with underlying phytoplankton photo-physiology. Additionally, ETR estimates are directly affected by photoprotective non-photochemical quenching (NPQ) that dissipates excess absorbed photo-energy as heat. Chapter 3 investigates the effects of photo-physiology and photo-acclimation states on NPQ relaxation time-scales, providing useful insights for field protocol design for high resolution ETR acquisition. In addition to NPQ, phytoplankton mitigate dangerous accumulation of reductant by diverting electrons towards alternative sinks, decoupling electron transport rates from downstream carbon fixation. Chapter 4 illustrates how this effect manifests as a hyperbolic relationship between ETR and carbon fixation, offering a new approach to predict carbon fixation rates from ETR. The work presented in this thesis addresses specific details of FRRF application, as well as broader questions regarding energy transfer efficiencies between photosynthetic processes, supporting the expansion of high-resolution FRRF-based estimates of biological carbon uptake.

Text

2025-04-25

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/90804

Oceanography

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/