Wind-driven upwelling followed by relaxation results in cycles of cold nutrient-rich water fueling intense phytoplankton blooms followed by nutrient-depletion, bloom decline, and sinking of cells. Surviving cells at depth can then be vertically transported back to the surface with upwelled waters to seed another bloom. As a result of these cycles, phytoplankton communities in upwelling regions are transported through a wide range of light and nutrient conditions. Diatoms appear to be well-suited for these cycles, but their responses to them remain understudied. To investigate the bases for diatoms' ecological success in upwelling environments, we employed laboratory simulations of a complete upwelling cycle with a common diatom, Chaetoceros decipiens, and coccolithophore, Emiliania huxleyi. We show that while both organisms exhibited physiological and transcriptomic plasticity, the diatom displayed a distinct response enabling it to rapidly shift-up growth rates and nitrate assimilation when returned to light and available nutrients following dark, nutrient-deplete conditions. As observed in natural diatom communities, C. decipiens highly expresses before upwelling, or frontloads, key transcriptional and nitrate assimilation genes coordinating its rapid response to upwelling conditions. Low iron simulations showed that C. decipiens is capable of maintaining this response when iron is limiting to growth, whereas E. huxleyi is not. Differential expression between iron treatments further revealed specific genes used by each organism under low iron availability. Overall, these results highlight the responses of two dominant phytoplankton groups to upwelling cycles, providing insight into the mechanisms fueling diatom blooms during upwelling events.

中文翻译：

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代表性的硅藻和球石藻物种在整个模拟上升周期中表现出不同的响应

风驱动的上升流随后是松弛，导致富含营养的冷水循环，促使强烈的浮游植物水华，随后营养物耗竭，水华下降和细胞下沉。然后，可以将深处存活的细胞与上升流一起垂直运回地面，以播种另一种花。这些循环的结果是，上升流区的浮游植物群落通过各种光照和营养条件运输。硅藻似乎很适合这些周期，但对它们的反应仍未得到充分研究。为了研究硅藻在上升环境中的生态成功基础，我们采用了一个完整的上升周期的实验室模拟，其中包括一个普通的硅藻Chaetoceros decipiens和球石藻，Emililiania huxleyi。我们显示，虽然两种生物都表现出生理和转录组可塑性，但硅藻显示出独特的响应，使其在黑暗，营养耗尽的条件下恢复光明和可用营养素时，能够迅速提高生长速度并吸收硝酸盐。如在自然硅藻群落中观察到的，C。decipiens在上涌或前负荷之前高表达协调其对上涌条件的快速响应的关键转录和硝酸盐同化基因。低铁模拟表明C.杜英能够当铁被限制到生长，维持该响应的，而E.贺胥不是。铁处理之间的差异表达进一步揭示了每种生物在低铁利用率下使用的特定基因。总体而言，这些结果突显了两个主要的浮游植物群对上升周期的响应，从而洞悉了在上升事件中助长硅藻绽放的机理。