The Southern Ocean (SO) harbours some of the most intense phytoplankton blooms on Earth. Changes in temperature and iron availability are expected to alter the intensity of SO phytoplankton blooms, but little is known about how environmental change will influence community composition and downstream biogeochemical processes. We performed experimental manipulations on surface ocean microbial communities from McMurdo Sound in the Ross Sea, with and without iron addition, at -0.5 °C, 3 °C, and 6 °C. We then examined nutrient uptake patterns as well as the growth and molecular responses of two dominant diatoms, Fragilariopsis and Pseudo-nitzschia, to these conditions. We found that nitrate uptake and primary productivity were elevated at increased temperature in the absence of iron addition, and were even greater at high temperature with added iron. Pseudo-nitzschia became more abundant under increased temperature without added iron, while Fragilariopsis required additional iron to benefit from warming. We attribute the apparent advantage Pseudo-nitzschia shows under warming to upregulation of iron-conserving photosynthetic processes, utilization of iron-economic nitrogen assimilation mechanisms, and increased iron uptake and storage. These data identify important molecular and physiological differences between dominant diatom groups and add to the growing body of evidence for Pseudo-nitzschia′s increasingly important role in warming SO ecosystems. This study also suggests that temperature-driven shifts in SO phytoplankton assemblages may increase utilization of the vast pool of excess nutrients in iron-limited SO surface waters, and thereby influence global nutrient distributions and carbon cycle.

中文翻译：

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南部海洋变暖中硅藻生长增强的分子基础和生物地球化学后果

南大洋（SO）拥有一些地球上最强烈的浮游植物水华。温度和铁利用率的变化有望改变SO浮游植物开花的强度，但人们对环境变化如何影响群落组成和下游生物地球化学过程知之甚少。我们在-0.5°C，3°C和6°C下对罗斯海麦克默多峡湾的表层海洋微生物群落进行了实验处理，添加和不添加铁。然后，我们检查了养分吸收模式以及两个主要的硅藻，脆藻和拟南芥的生长和分子响应。，以适应这些条件。我们发现，在不添加铁的情况下，温度升高时，硝酸盐的吸收和初级生产力会提高，而在添加铁的情况下，硝酸盐的吸收和初级生产力会更高。在不添加铁的情况下，温度升高时假尼丝球菌变得更丰富，而脆皮紫薇需要更多的铁才能从变暖中受益。我们归因于伪尼兹卡菌在变暖下表现出的明显优势归因于铁保护性光合作用过程的上调，铁-经济氮同化机制的利用以及铁吸收和储存的增加。这些数据确定了主要硅藻类之间重要的分子和生理差异，并增加了越来越多的证据表明拟南芥在温暖SO生态系统中的作用越来越重要。这项研究还表明，SO浮游植物组合中温度驱动的变化可能会增加铁限制的SO地表水中大量过量养分的利用，从而影响全球养分分布和碳循环。