Sea ice retreat, changing stratification, and ocean acidification are fundamentally changing the light availability and physico-chemical conditions for primary producers in the Arctic Ocean. However, detailed studies on ecophysiological strategies and performance of key species in the pelagic and ice-associated habitat remain scarce. Therefore, we investigated the acclimated responses of the diatoms Thalassiosira hyalina and Melosira arctica toward elevated irradiance and CO₂ partial pressures (pCO₂). Next to growth, elemental composition, and biomass production, we assessed detailed photophysiological responses through fluorometry and gas-flux measurements, including respiration and carbon acquisition. In the pelagic T. hyalina, growth rates remained high in all treatments and biomass production increased strongly with light. Even under low irradiances cells maintained a high-light acclimated state, allowing them to opportunistically utilize high irradiances by means of a highly plastic photosynthetic machinery and carbon uptake. The ice-associated M. arctica proved to be less plastic and more specialized on low-light. Its acclimation to high irradiances was characterized by minimizing photon harvest and photosynthetic efficiency, which led to lowered growth. Comparably low growth rates and strong silification advocate a strategy of persistence rather than of fast proliferation, which is also in line with the observed formation of resting stages under low-light conditions. In both species, responses to elevated pCO₂ were comparably minor. Although both diatom species persisted under the applied conditions, their competitive abilities and strategies differ strongly. With the anticipated extension of Arctic pelagic habitats, flexible high-light specialists like T. hyalina seem to face a brighter future.

中文翻译：

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高光和 pCO2 下的远洋和冰相关微藻：两种北极硅藻的生理策略对比

海冰退缩、分层变化和海洋酸化正在从根本上改变北冰洋初级生产者的光照可用性和物理化学条件。然而，关于远洋和冰相关生境中关键物种的生态生理策略和表现的详细研究仍然很少。因此，我们研究了硅藻Thalassiosira hyalina和Melosira arctica对升高的辐照度和 CO ₂分压 (pCO ₂ ) 的适应反应。除了生长、元素组成和生物量生产之外，我们还通过荧光测量和气体通量测量（包括呼吸和碳获取）评估了详细的光生理反应。在远洋T. hyalina，所有处理中的生长速率都保持很高，并且生物量产量随光照强烈增加。即使在低辐照度下，细胞也能保持高光适应状态，从而使它们能够通过高度可塑性的光合作用机制和碳吸收来机会性地利用高辐照度。与冰相关的M. arctica事实证明，塑料更少，更专注于低光。它对高辐照度的适应的特点是最大限度地减少光子收获和光合效率，从而导致生长降低。相对较低的生长速率和强烈的硅化提倡一种持久而不是快速增殖的策略，这也符合在弱光条件下观察到的静止阶段的形成。_{在这两个物种中，对 pCO 2}升高的反应相对较小。尽管两种硅藻物种在应用条件下都存在，但它们的竞争能力和策略差异很大。随着北极中上层栖息地的预期扩展，像海亚利娜（ T. hyalina ）这样灵活的高光专家似乎面临着更光明的未来。