Iron and temperature are important drivers controlling phytoplankton growth in the Southern Ocean (SO). Most studies examining phytoplankton responses to these variables consider them independently, testing responses to changing temperature under constant iron and vice versa. Consequently, we lack a phenomenological and mechanistic understanding of how concurrent changes in these variables influence primary productivity. Here, we used a matrix of three temperatures and eight iron levels to examine changes in growth rate, photophysiology, and size in Fragilariopsis cylindrus. Temperature and iron interactively influenced growth; warming decreased iron demand, allowing cells to maintain half‐maximal growth rate at lower iron concentrations. We also observed possible mechanisms underpinning this phenomenon: warming increased light‐harvesting cross section and reduced cell size, thereby increasing light energy availability and iron uptake efficiency. These results suggest that interactive iron‐warming effects could lead to larger increases in SO phytoplankton growth than those currently predicted by marine ecosystem models.

中文翻译：

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铁和温度对水曲柳生长的交互作用

铁和温度是控制南大洋浮游植物生长的重要驱动力。大多数研究浮游植物对这些变量的反应的研究都是独立考虑它们的，在恒定铁的条件下测试对温度变化的反应，反之亦然。因此，我们对这些变量的同时变化如何影响初级生产力缺乏现象学和机械学的理解。在这里，我们使用了三个温度和八个铁水平的矩阵来检查生长在圆柏中的生长速率，光生理学和大小的变化。温度和铁相互作用地影响生长；变暖降低了铁的需求量，使细胞在较低的铁浓度下保持半数最大的生长速率。我们还观察到了造成这种现象的可能机制：升温增加了采光截面并减小了细胞大小，从而增加了光能利用率和铁吸收效率。这些结果表明，相互作用的铁温效应可能导致SO浮游植物的增长比海洋生态系统模型目前预测的更大。