Optimality-based model of phytoplankton growth and diazotrophy.

Pahlow, Markus, Dietze, Heiner and Oschlies, Andreas (2013) Optimality-based model of phytoplankton growth and diazotrophy. Open Access Marine Ecology Progress Series, 489 . pp. 1-16. DOI 10.3354/meps10449.

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The notion that excess phosphorus (P) and high irradiance favour pelagic diazotrophy is difficult to reconcile with diazotroph behaviour in laboratory experiments and also with the observed distribution of N2-fixing Trichodesmium, e.g. in the relatively nitrogen (N)-rich North Atlantic Ocean. Nevertheless, this view currently provides the state-of-the-art framework to understand both past dynamics and future evolution of the oceanic fixed N inventory. In an attempt to provide a consistent theoretical underpinning for marine autotrophic N2 fixation we derive controls of diazotrophy from an optimality-based model that accounts for phytoplankton growth and N2 fixation. Our approach differs from existing work in that conditions favourable for diazotrophy are not prescribed but emerge, indirectly, from trade-offs among energy and cellular resource requirements for the acquisition of P, N, and carbon. Our model reproduces laboratory data for a range of ordinary phytoplankton species and Trichodesmium. The model predicts that (1) the optimal strategy for facultative diazotrophy is switching between N2 fixation and using dissolved inorganic nitrogen (DIN) at a threshold DIN concentration; (2) oligotrophy, especially in P and under high light, favours diazotrophy; (3) diazotrophy is compatible with DIN:DIP supply ratios well above Redfield proportions; and (4) communities of diazotrophs competing with ordinary phytoplankton decouple emerging ambient and supply DIN:DIP ratios. Our model predictions appear in line with major observed patterns of diazotrophy in the ocean. The predicted importance of oligotrophy in P extends the present view of N2 fixation beyond a simple control by excess P in the surface ocean.

Document Type: Article
Funder compliance: info:eu-repo/grantAgreement/EC/FP7/282723
Additional Information: WOS:000323941000001 FP7-SPACE-2011-282723
Keywords: Nitrogen fixation; Phytoplankton; Optimality; Chain model; Resource allocation; Elemental composition
Research affiliation: OceanRep > SFB 754 > B2
OceanRep > SFB 754
OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-BM Biogeochemical Modeling
Refereed: Yes
Open Access Journal?: No
Publisher: Inter Research
Projects: SPACE, SFB754, Future Ocean
Date Deposited: 26 Sep 2013 08:26
Last Modified: 24 Sep 2019 00:11
URI: https://oceanrep.geomar.de/id/eprint/22033

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