Phytoplankton Photochemical Budgets: Translating Optical Measurements to Productivity

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Detailed measurements of phytoplankton photosynthesis using mass spectrometry, variable fluorescence, and light absorption have detected a significant energy loss process under light saturation conditions. The energy loss to productivity is tentatively identified as cyclic electron flow around photosystem II. This phenomenon alters the relationship between the quantum yields of carbon assimilation, oxygen evolution, and photosystem II, making fluorescence-based estimates of primary productivity (carbon-based) inaccurate. The research willcharacterize specific environmental conditions (fluctuating light and nutrient availability) that are expected to affect the expression of this process. Experiments will be conducted on six taxonomically diverse microalgal species using O-18 mass spectrometry, C-14 bicarbonate assimilation, variable fluorescence, and light absorption measurements to measure a) total electron flow through photosystem II, b) true gross oxygen evolution, c) light dependent oxygenuptake, and d) carbon assimilation. These data will be used to partition the energy flow between light absorption, photochemical activity, non-cyclic electron transport, and electron transport to carbon production, thereby identifying the magnitude and environmental control of energy dissipation processes that are hidden from conventional methods. The project has a significant bearing on the use of bio-optical and fluorescence methods used in Biological Oceanography to assess primary productivity remotely and in situ.