SGER: Assessing Nutrient Limitation of Phytoplankton Photosynthesis

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This project examines the applicability of a newly developed bio- optical instrument (pump and probe fluorometer) that may be able to measure the "health" of oceanic phytoplankton. In theory, this instrument provides a means for non-destructive measurement of phytoplankton photosynthesis without recourse to calibration against standard biological measurements. The technique, if successfully proven, will be able to establish the nutrient status of phytoplankton from measurements of photosynthetic efficiency. Present studies indicate that photosynthetic efficiency of phytoplankton is independent of temperature and irradiance under nutrient replete conditions, but decreases under nutrient limitation. This project is designed to thoroughly test the instrument under controlled laboratory conditions using three different species of phytoplankton whose growth rates are controlled by limiting nitrate, phosphate, silicate, and iron. Such information is crucial to the development of a quantitative understanding of environmental regulation of primary productivity in the sea.