Phytoplankton growth in the ocean amounts to about half of global primary production. Nitrogen (N) is an essential element for all life in the ocean, and primary productivity is limited by the availability of N in the vast majority of the ocean. On long time scales, biological dinitrogen (N2) fixation is yet the largest source of new N to the ocean and thus exerts control over export production and the sequestration of atmospheric carbon dioxide (CO2). Despite the importance of N2 fixation for the global ocean, there is still a lack of knowledge about the regulatory mechanisms, the key players, and the extent of N2 fixation in the ocean.
My particular research interests therefore address the following topics:
- N2 fixation activity in nutrient-limited aquatic systems, particularly the open ocean
- Identification of relevant N2-fixing microorganisms (diazotrophs)
- Detection and activity measurements of diazotrophs in the environment
- Regulation of N2 fixation at the single-cell, population and environmental level
In order to target these topics, my research employs geochemical, microbiological, molecular and single-cell techniques such as stable isotope incubations, cultivation, high-throughput sequencing, and nanometer-scale secondary ion mass spectrometry (nanoSIMS).