Recent published work presented evidence that marine diatoms use a C4 pathway to concentrate carbon dioxide (CO2) for fixation through photosynthesis (i.e. based on 4-carbon intermediate compounds, as opposed to a C3 pathway based on 3-carbon intermediates). The goal of this project is to examine the role of this mechanism in the acclimation of photosynthetic carbon fixation in marine diatoms to low CO2, and the modulation of this acclimation by light and nutrient limitation. Laboratory experiments will focus on quantifying C4 gene transcript abundances and enzyme activities in short-term experiments and in light-dark cycle and light- and nitrogen-limited cultures of model diatom species. Fieldwork will focus on examining the importance of the C4 concentrating mechanism and its regulation by CO2 in an upwelling region off the coast of Oregon characterized by a naturally wide range of CO2 concentrations. The field experimental approach will be to measure the sensitivities of photosynthetic carbon fixation in natural diatom populations to the inhibition of C4 enzymes, in relation to in situ and manipulated concentrations of CO2. The regulation of carbon fixation in marine diatoms by carbon dioxide (CO2) and the modulation of CO2 control by light and nutrients may affect ocean productivity, biological carbon export from surface waters and therefore the contribution of diatoms to global carbon cycling, and phytoplankton species composition. The results of this research will be of interest to oceanographers studying the controls of primary production and the biological carbon pump, geochemists interested in the use of stable carbon isotopes in diatom organic matter to understand current and historic productivity and climate change, and marine ecologists interested in the structure and evolution of phytoplankton communities. The project will support and train a graduate student as well as provide research opportunities for undergraduates. The researchers will also incorporate undergraduate students from the NSF-funded RIOS summer internship program into this project and will support the public outreach and education efforts of the newly established Mid-Atlantic Center for Ocean Science Education Excellence.
