Concentrations of bioavailable inorganic nitrogen (N) and phosphorus (P) are simultaneously depleted in the (sub)tropical North Atlantic Ocean, but it remains unclear if phytoplankton growth rates are N limited or N–P co‐limited. Here we present findings from three bottle‐scale experiments using a four‐by‐four matrix of low‐level N and P additions, conducted at one site in the subtropical North Atlantic Ocean. Phytoplankton responses were assessed both in terms of bulk chlorophyll a (Chl a) concentrations and intracellular Chl a of dominant Prochlorococcus and Synechococcus groups. Two matrix experiments suggested that N was independently limiting in situ growth, with no co‐limiting role for P, while the third showed co‐limitation by both N and P in this region. This switch from N limitation to N–P co‐limitation was attributed to an episodic wet deposition event that supplied N, thereby stimulating phytoplankton growth and consuming available P. Such rapid transitions in nutrient limitation in response to environmental forcing might be common in oceanic systems with multiple depleted nutrients.

中文翻译：

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北大西洋副热带氮限制与氮磷共限制之间的转换

在北大西洋（亚）热带地区，生物可利用的无机氮（N）和磷（P）浓度同时减少，但目前尚不清楚浮游植物的生长速度是受氮限制还是受氮磷共同限制。在这里，我们展示了在北大西洋亚热带的一个地点进行的三个瓶规模实验的结果，这些实验使用了低水平氮和磷添加的四乘四矩阵。浮游植物反应根据大量叶绿素进行评估A（叶绿素A) 浓度和细胞内叶绿素A占主导地位的原绿球藻和聚球藻属组。两个基质实验表明，N 独立限制原位生长，对 P 没有共同限制作用，而第三个实验表明 N 和 P 在此区域共同限制。这种从氮限制到氮磷共同限制的转变归因于间歇性湿沉降事件，该事件提供氮，从而刺激浮游植物生长并消耗可用磷。这种因环境强迫而导致的营养限制的快速转变可能在海洋系统中很常见与多种营养物质耗尽。