Phytoplankton are key players in global biogeochemical cycles, and the effects of ocean warming on their carbon–nitrogen–phosphorus (CNP) stoichiometry, photosynthesis, size, morphology, growth rates, and other traits are of great ecological consequence. The physiological mechanisms of adaptation to temperature in phytoplankton are poorly understood, as are the consequences of the evolution of these processes (e.g., nutrient uptake, photosynthesis) for global biogeochemistry. In general, high temperatures favor smaller cells with higher surface area-to-volume ratios, but repeatable patterns in cellular CNP stoichiometry across temperature remain elusive. Here, we compared thermal reaction norms for cellular C, N, P, and chlorophyll a (Chl a) content and for carbon assimilation rate in replicate populations of the marine diatom Thalassiosira pseudonana evolved for 500 generations at 16°C and 31°C. We also examined the thermal reaction norms for cell volume and morphological traits. T. pseudonana has a cylindrical frustule and likely primarily exchanges materials with the environment through the round valve faces. We found that the 31°C-selected T. pseudonana populations had smaller cells and higher per-biovolume densities of nutrients and Chl a than the 16°C-selected populations across assay temperatures but there were no detectable patterns in CNP stoichiometry. The 31°C-selected populations also had higher valve surface area-to-cell volume ratio that increased more with temperature, suggesting better nutrient uptake capabilities than in the 16°C-selected populations. Our study demonstrates that temperature-dependent physiological plasticity may evolve differently at different temperatures and suggests that future phytoplankton communities will consist of smaller, more nutrient-dense cells.

中文翻译：

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海洋硅藻中细胞形态和碳和营养成分的温度依赖性演化

浮游植物是全球生物地球化学循环的关键参与者，海洋变暖对其碳氮磷 (CNP) 化学计量、光合作用、大小、形态、生长速率和其他特性的影响具有重大的生态后果。对浮游植物适应温度的生理机制知之甚少，这些过程（例如，养分吸收、光合作用）的进化对全球生物地球化学的影响也是如此。一般来说，高温有利于具有更高表面积与体积比的较小细胞，但细胞 CNP 化学计量在温度范围内的可重复模式仍然难以捉摸。在这里，我们比较了细胞 C、N、P 和叶绿素a（Chl a）含量和在海洋硅藻的复制群体碳同化率海链pseudonana在16℃和31°C进化为500代。我们还检查了细胞体积和形态特征的热反应规范。T. pseudonana具有圆柱形硅藻壳，可能主要通过圆形阀面与环境进行物质交换。我们发现 31°C 选择的T. pseudonana种群具有更小的细胞和更高的每生物体积密度的营养物质和 Chl a与 16°C 选择的群体在测定温度下相比，但在 CNP 化学计量学中没有可检测的模式。31°C 选择的种群还具有更高的瓣膜表面积与细胞体积比，随着温度的增加而增加更多，这表明比 16°C 选择的种群具有更好的养分吸收能力。我们的研究表明，温度依赖性生理可塑性在不同温度下可能会发生不同的演变，并表明未来的浮游植物群落将由更小、营养更密集的细胞组成。