Optimality-based model of phytoplankton growth and diazotrophy

Marine Ecology Progress Series

Markus Pahlow¹  Andreas Oschlies¹  Heiner Dietze¹ 

关键词: Nitrogen fixation;    Phytoplankton;    Optimality;    Chain model;    Resource allocation;    Elemental composition;   

DOI  :  10.3354/meps10449

学科分类：海洋学与技术

来源: Inter-Research

【 摘 要 】

ABSTRACT: 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.

【 授权许可】

Unknown