Coastal upwelling currents such as the California Current System (CCS) comprise some of the most productive biological systems on the planet. Diatoms dominate these upwelling events in part due to their rapid response to nutrient entrainment. In this region, they may also be limited by the micronutrient iron (Fe), an important trace element primarily involved in photosynthesis and nitrogen assimilation. The mechanisms behind how diatoms physiologically acclimate to the different stages of the upwelling conveyor belt cycle remain largely uncharacterized. Here, we explore their physiological and metatranscriptomic response to the upwelling cycle with respect to the Fe limitation mosaic that exists in the CCS. Subsurface, natural plankton assemblages that would potentially seed surface blooms were examined over wide and narrow shelf regions. The initial biomass and physiological state of the phytoplankton community had a large impact on the overall response to simulated upwelling. Following on‐deck incubations under varying Fe physiological states, our results suggest that diatoms quickly dominated the blooms by “frontloading” nitrogen assimilation genes prior to upwelling. However, diatoms subjected to induced Fe limitation exhibited reductions in carbon and nitrogen uptake and decreasing biomass accumulation. Simultaneously, they exhibited a distinct gene expression response which included increased expression of Fe‐starvation induced proteins and decreased expression of nitrogen assimilation and photosynthesis genes. These findings may have significant implications for upwelling events in future oceans, where changes in ocean conditions are projected to amplify the gradient of Fe limitation in coastal upwelling regions.

中文翻译：

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浮游植物对加州洋流系统内铁限制马赛克上涌反应的变异性

加利福尼亚洋流系统 (CCS) 等沿海上升流构成了地球上一些生产力最高的生物系统。硅藻在这些上升流事件中占主导地位，部分原因是它们对营养物夹带的快速反应。在这个区域，它们也可能受到微量营养素铁 (Fe) 的限制，铁是一种主要参与光合作用和氮同化的重要微量元素。硅藻如何在生理上适应上升传送带周期的不同阶段背后的机制在很大程度上仍然未知。在这里，我们探讨了它们对 CCS 中存在的 Fe 限制马赛克的上升循环的生理和宏转录组反应。在宽阔和狭窄的陆架区域检查了可能在表面繁殖的地下天然浮游生物组合。浮游植物群落的初始生物量和生理状态对模拟上升流的整体响应有很大影响。在不同铁生理状态下的甲板上孵化后，我们的结果表明，硅藻在上升之前通过“前载”氮同化基因迅速控制了水华。然而，受到诱导铁限制的硅藻表现出碳和氮吸收的减少以及生物量积累的减少。同时，它们表现出独特的基因表达反应，包括铁饥饿诱导蛋白的表达增加以及氮同化和光合作用基因的表达减少。这些发现可能对未来海洋的上升流事件产生重大影响，预计海洋条件的变化将放大沿海上升流区域铁限制的梯度。