N2 fixation in global marine biogeochemical models: Can trade-offs in modelled phosphorus acquisition strategies resolve the marine N2 fixation paradox?

• Applicant: Dr. Angela Landolfi
• Subject Area: Oceanography
• Term: from 2011 to 2014
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 192813937

Slowly growing N2 fixers may out-compete non-fixing phytoplankton only in N-limited ecosystems. This paradigm has forged the way N2 fixation is parameterized in global marine biogeochemical models. However, state-of-the-art global coupled circulation-ecosystem models fail to reproduce the paradoxical observations of high N2 fixation rates in N-rich areas like the tropical North Atlantic. This constrains our ability to predict global patterns of marine N2 fixation in a changing world. We propose to incorporate the recent physiological understanding of marine diazotrophs into a global biogeochemical ocean circulation model and assess the simulated diazotroph’s sensitivity to environmental changes. A cost-benefit approach will be used to asses the role of trade-offs inherent to the acquisition of dissolved organic phosphorus (DOP), i.e. the benefit of using DOP requiring enzymatic N investments at an extra metabolic cost. We hypothesize that marine N2 fixers may exploit the unlimited N2 reservoir to synthesize hydrolytic enzymes that can break down DOP. If this hypothesis proves true, it may explain high N2 fixation rates in N-rich areas and thereby improve the degree of realism of biogeochemical ocean models allowing to quantitatively investigate as yet un-forseen interactions between the oceanic nutrient cycles in response to environmental changes.

• DFG Programme: Research Grants
• Participating Person: Professor Dr. Andreas Oschlies