The combination of taxa and size classes of phytoplankton that coexist at any location affects the structure of the marine food web and the magnitude of carbon fluxes to the deep ocean. But what controls the patterns of this community structure across environmental gradients remains unclear. Here, we focus on the North East Pacific Transition Zone, a ~ 10° region of latitude straddling warm, nutrient‐poor subtropical and cold, nutrient‐rich subpolar gyres. Data from three cruises to the region revealed intricate patterns of phytoplankton community structure: poleward increases in the number of cell size classes; increasing biomass of picoeukaryotes and diatoms; decreases in diazotrophs and Prochlorococcus; and both increases and decreases in Synechococcus. These patterns can only be partially explained by existing theories. Using data, theory, and numerical simulations, we show that the patterns of plankton distributions across the transition zone are the result of gradients in nutrient supply rates, which control a range of complex biotic interactions. We examine how interactions such as size‐specific grazing, multiple trophic strategies, shared grazing between several phytoplankton size classes and heterotrophic bacteria, and competition for multiple resources can individually explain aspects of the observed community structure. However, it is the combination of all these interactions together that is needed to explain the bulk compositional patterns in phytoplankton across the North East Pacific Transition Zone. The synthesis of multiple mechanisms is essential for us to begin to understand the shaping of community structure over large environmental gradients.

中文翻译：

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多种生物相互作用建立了跨环境梯度的浮游植物群落结构

在任何地点共存的浮游植物的类群和大小类别的组合会影响海洋食物网的结构和深海碳通量的大小。但是什么控制着这种跨环境梯度的群落结构模式仍不清楚。在这里，我们重点关注东北太平洋过渡带，这是一个纬度约 10° 的区域，横跨温暖、营养贫乏的亚热带和寒冷、营养丰富的副极地环流。来自对该地区的三次航行的数据揭示了浮游植物群落结构的复杂模式：细胞大小类别数量向极地增加；增加超微核生物和硅藻的生物量；固氮菌减少和原绿球藻;并且都增加和减少聚球藻属。现有理论只能部分解释这些模式。利用数据、理论和数值模拟，我们表明过渡区浮游生物的分布模式是养分供应率梯度的结果，养分供应率控制着一系列复杂的生物相互作用。我们研究了特定大小的放牧、多种营养策略、几种浮游植物大小类别和异养细菌之间的共享放牧以及对多种资源的竞争等相互作用如何能够单独解释所观察到的群落结构的各个方面。然而，需要将所有这些相互作用结合在一起来解释东北太平洋过渡区浮游植物的总体组成模式。多种机制的综合对于我们开始理解大环境梯度下群落结构的形成至关重要。