ABSTRACT

Intellectual merit. Marine phytoplankton are a diverse group of Prokaryotic and Eukaryotic unicellular organisms that account for approximately 50% of global carbon fixation. Nitrogen (N) is an essential element for microbial growth, but concentrations of bioavailable nitrogen in vast regions of subtropical ocean gyres are extremely low (submicromolar to nanomolar concentrations), and generally limit phytoplankton growth. Phytoplankton taxa differ in their genetic capabilities to take up and assimilate nutrients, and thus competition for different chemical forms of N (NH4+, NO3- and urea) and supply of these N-containing compounds are important controls on phytoplankton growth, productivity, and ultimately ecosystem function. The form and supply of N to phytoplankton have already been altered by anthropogenic activities, and with increasing environmental perturbations the effects will accelerate. To date however, there is limited information on how the N forms and fluxes impact the marine phytoplankton community composition and primary production. Similarly, determining the mechanisms of the response are crucial to assessing how ocean ecosystem function will respond to global climate change. This project seeks to determine how taxonomic, genetic and functional dimensions of phytoplankton diversity are linked with community-level responses to the availability of different N substrates (NH4+, NO3-, and urea) in one of Earth's largest aquatic habitats, the North Pacific Subtropical Gyre. The project will characterize phytoplankton community composition change and gene expression, photosynthetic performance, carbon fixation, and single-cell level N and C uptake in different taxa within the phytoplankton assemblage in response to different N compounds. The research project is unique in investigating community-to-single-cell level function and species (strain)-specific gene expression patterns using state-of-the-art methods including fast repetition rate fluorometry, nanoscale secondary ion mass spectrometry and a comprehensive marine microbial community microarray. The results will provide predictive understanding of how changes in the availability of key nitrogen pools (N) may impact phytoplankton dynamics and function in the ocean.

Broader impacts. This project seeks to understand the ecological basis linking the metabolism of N to phytoplankton biodiversity in the open ocean. The underlying concept that links ecological competition for nutrients (in this case N) to phytoplankton diversity will provide a universal framework for understanding how ecosystem functions are linked to biodiversity. By applying state-of-the-art molecular and genetic methods to address ecological questions, the project seeks to develop an innovative workflow to assess eukaryotic and prokaryotic gene functions in the environment, and provides modern analytical and bioinformatic training for graduate students and postdoctoral researchers. The microarray tool has been designed by involving the larger marine microbiology community and is available to the greater scientific community, and this project is one of the first implementations. The fundamental concepts of microbial ecology and genomics will be used in educational activities in undergraduate and graduate-level classes as well as research training for undergraduates and graduates. Students and the postdoctoral researcher supported by this project will be engaged in development of microbiological and molecular biological displays and presentations at the Exploratorium, a science museum in San Francisco, California. Project personnel will collaboratively develop modules for the Exploratorium. The Exploratorium partnership will provide a mechanism for educational outreach for students and post-docs, as well as an efficient means to communicate the importance of ocean microbes and genomics to the public (over 600,000 visitors per year). The PIs will work with the education team in the Center for Microbial Oceanography: Research and Education (C-MORE) scholars program, at the University of Hawaii, to recruit an undergraduate student to participate in this project. The C- MORE scholars program seeks to promote workforce diversity by identifying faculty mentors to work with students of traditionally underrepresented backgrounds in the STEM disciplines.

Integration. This project integrates multiple perspectives on microbial biodiversity. The project seeks to understand how nitrogenous nutrients regulate the taxonomic, genetic, and functional diversity of phytoplankton communities through differential gene expression and functional properties of phytoplankton taxa.

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