Graduate Thesis Or Dissertation
 

Photoacclimation in Marine Phytoplankton Under Various Light and Nutrient Regimes and the Resulting Effect on Photosynthetic Electron Flow and Chlorophyll Fluorescence Transients

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  • Photoacclimation is the process by which plants and phytoplankton adjust the concentration and composition of their photosynthetic machinery (i.e. their photoacclimation state) in response to changes in their light or nutrient environment. The purpose of photoacclimation is to balance the rate at which light energy is absorbed with the energetic needs of the cell. As a consequence, photoacclimation can affect the rate (at a given light level) at which electrons are utilized in photochemistry and can alter how photosynthetically-derived reductant is used in cellular metabolism. As such, modeling primary production within the marine environment requires an accurate understanding of photoacclimation. In my dissertation, I studied photoacclimation in several species of marine phytoplankton under a variety of light and nutrient growth regimes. By measuring chlorophyll fluorescence, I examined how photoacclimation under different environmental conditions alters the rate of electron flow through the photosynthetic electron transport chain. My experiments showed that the shape of the fluorescence transient (i.e. the curve produced by measuring fluorescence over time) varied predictably with growth irradiance in all species and that this reflected changes in the relative reduction and oxidation rates of the plastoquinone pool (electron carriers within the photosynthetic electron transport chain). In addition, I examined photoacclimation in the marine diatom Thalassiosira weissflogii under fluctuating light conditions simulating different mixing depths. My results show that photoacclimation state in this species is unaffected by periodic mixing into the dark beneath the photic zone (i.e. the illuminated area of the mixed layer). The results of my dissertation provide an improved understanding of the photoacclimation process under natural conditions.
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