Increasing dissolution of CO2 in the surface ocean is rapidly decreasing its pH and changing carbon chemistry which is further affecting marine biota in several ways. Phytoplankton response studies under the combination of elevated CO2 and trace metals are rare. We have conducted two consecutive onboard incubation experiments (R. V. Sindhu Sadhana; August 2017) in the eastern Arabian Sea (SW coast of India) during an upwelling event. A nutrient enriched diatom bloom was initiated onboard and grown under ambient (≈400 μatm, A-CO2) and high CO2 levels (≈1000 μatm; H-CO2) with different zinc (Zn; 1 nM) and copper (Cu) concentrations (1 nM, 2 nM and 8 nM). Phytoplankton community composition and the dominant genera were different during these two experiments. CO2 enrichment alone did not show any significant growth stimulating impact on the experimental community except enhanced cell density in the first experiment. Addition of Zn at A-CO2 level revealed no noticeable responses; whereas, the same treatment under H-CO2 level significantly reduced cell number. Considerably high protein content under H-CO2+Zn treatment was possibly counteracting Zn toxicity which also caused slower growth rate. Cu addition did not show any noticeable impact on growth and biomass production except increased protein content as well as decreased carbohydrate: protein ratio. This can be attributed to relatively higher protein synthesis than carbohydrate to alleviate oxidative stress generated by Cu. The centric diatom Chaetoceros and toxin producing pennate diatom Pseudo-nitzschia showed no significant response to either CO2 or Zn enrichment. Large centric diatom Leptocylindrus and Skeletonema responded positively to Zn addition in both CO2 levels. The former species showed the most sensitive response at the highest Cu and H-CO2 treatment; whereas, the pennate diatoms Nitzschia and Pseudo-nitzschia (toxigenic diatom) showed higher resilience under elevated CO2 and Cu levels. This observation indicated that in future ocean, increasing CO2 concentrations and trace metal pollution may potentially alter phytoplankton community structure and may facilitate toxigenic diatom bloom in the coastal waters.

中文翻译：

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海洋酸化情景下锌和铜的富集对热带上升系统中浮游植物群落的影响。

二氧化碳在表层海洋中溶解度的增加正在迅速降低其pH值并改变碳化学性质，从而以多种方式进一步影响海洋生物。二氧化碳和痕量金属结合的浮游植物反应研究很少。在一次上升流事件中，我们在阿拉伯海东部（印度西南海岸）进行了两个连续的船上孵化实验（RV Sindhu Sadhana; 2017年8月）。在船上启动了富含营养的硅藻绽放，并在环境（≈400μatm，A-CO2）和高CO2水平（≈1000μatm； H-CO2）下以不同的锌（Zn； 1 nM）和铜（Cu）浓度生长（ 1 nM，2 nM和8 nM）。在这两个实验中，浮游植物群落组成和优势属不同。除了第一个实验中增加的细胞密度外，单独的CO2富集对实验社区没有任何显着的生长刺激作用。在A-CO2水平上添加Zn并没有发现明显的反应。相反，在H-CO2水平下进行相同的处理可以显着减少细胞数。在H-CO2 + Zn处理下，相当高的蛋白质含量可能抵消了Zn的毒性，后者也导致了较慢的生长速度。铜的添加对蛋白质的生长和生物量的生产没有明显的影响，除了增加蛋白质含量以及减少碳水化合物：蛋白质比例。这可以归因于比碳水化合物相对更高的蛋白质合成，以减轻由铜产生的氧化应激。中心硅藻Chaetoceros和产生毒素的戊二酸酯硅藻假性尼兹菌对CO2或Zn富集均无明显反应。大型中心硅藻Leptocylindrus和Skeletonema在两个CO2水平上对锌的添加均呈阳性反应。前者在最高的Cu和H-CO2处理下表现出最敏感的响应。然而，在CO2和Cu水平升高的情况下，戊二烯硅藻Nitzschia和Pseudo-Nitzschia（产毒硅藻）显示出更高的弹性。该观察结果表明，在未来的海洋中，不断增加的CO2浓度和微量金属污染可能会改变浮游植物的群落结构，并可能促进沿海水域的产毒硅藻绽放。前者在最高的Cu和H-CO2处理下表现出最敏感的响应。然而，在CO2和Cu水平升高的情况下，戊二烯硅藻Nitzschia和Pseudo-Nitzschia（产毒硅藻）显示出更高的弹性。该观察结果表明，在未来的海洋中，不断增加的CO2浓度和痕量金属污染可能会改变浮游植物的群落结构，并可能促进沿海水域的产毒硅藻绽放。前者在最高的Cu和H-CO2处理下表现出最敏感的响应。然而，在CO2和Cu水平升高的情况下，戊二烯硅藻Nitzschia和Pseudo-Nitzschia（产毒硅藻）显示出更高的弹性。该观察结果表明，在未来的海洋中，不断增加的CO2浓度和微量金属污染可能会改变浮游植物的群落结构，并可能促进沿海水域的产毒硅藻绽放。