Abstract An indoor mesocosm experiment was carried out to investigate the combined effects of ocean acidification and warming on the species composition and biogeochemical element cycling during a winter/spring bloom with a natural phytoplankton assemblage from the Kiel fjord, Germany. The experimental setup consisted of a “Control” (ambient temperature of ~4.8 °C and ~535 ± 25 μatm pCO2), a “High-CO2” treatment (ambient temperature and initially 1020 ± 45 μatm pCO2) and a “Greenhouse” treatment (~8.5 °C and initially 990 ± 60 μatm pCO2). Nutrient replete conditions prevailed at the beginning of the experiment and light was provided at in situ levels upon reaching pCO2 target levels. A diatom-dominated bloom developed in all treatments with Skeletonema costatum as the dominant species but with an increased abundance and biomass contribution of larger diatom species in the Greenhouse treatment. Conditions in the Greenhouse treatment accelerated bloom development with faster utilization of inorganic nutrients and an earlier peak in phytoplankton biomass compared to the Control and High CO2 but no difference in maximum concentration of particulate organic matter (POM) between treatments. Loss of POM in the Greenhouse treatment, however, was twice as high as in the Control and High CO2 treatment at the end of the experiment, most likely due to an increased proportion of larger diatom species in that treatment. We hypothesize that the combination of warming and acidification can induce shifts in diatom species composition with potential feedbacks on biogeochemical element cycling.

中文翻译：

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在高二氧化碳和变暖条件下，天然浮游植物组合中向更大的硅藻转变

摘要 为了研究德国基尔峡湾的天然浮游植物组合在冬季/春季水华期间海洋酸化和变暖对物种组成和生物地球化学元素循环的综合影响，进行了室内中宇宙实验。实验设置包括“控制”（环境温度约 4.8 °C 和约 535 ± 25 μatm pCO2）、“高 CO2”处理（环境温度和最初 1020 ± 45 μatm pCO2）和“温室”处理（~8.5 °C 和最初 990 ± 60 μatm pCO2）。在实验开始时营养充足的条件占主导地位，并且在达到 pCO2 目标水平后就地提供光照。在以中肋骨骨架为优势物种的所有处理中都出现了以硅藻为主的水华，但在温室处理中较大的硅藻物种的丰度和生物量贡献增加。与对照和高 CO2 相比，温室处理中的条件加速了水华发展，无机养分的利用更快，浮游植物生物量的峰值更早，但处理之间的颗粒有机物质 (POM) 的最大浓度没有差异。然而，在实验结束时，温室处理中 POM 的损失是对照和高 CO2 处理中的两倍，这很可能是由于该处理中较大硅藻物种的比例增加。