In the Southern Ocean (SO), iron (Fe) limitation strongly inhibits phytoplankton growth and generally decreases their primary productivity. Diatoms are a key component in the carbon (C) cycle, by taking up large amounts of anthropogenic CO 2 through the biological carbon pump. In this study, we investigated the effects of Fe availability (no Fe and 4 nM FeCl 3 addition) on the physiology of Chaetoceros cf. simplex , an ecologically relevant SO diatom. Our results are the first combining oxygen evolution and uptake rates with particulate organic carbon (POC) build up, pigments, photophysiological parameters and intracellular trace metal (TM) quotas in an Fe-deficient Antarctic diatom. Decreases in both oxygen evolution (through photosynthesis, P) and uptake (respiration, R) coincided with a lowered growth rate of Fe-deficient cells. In addition, cells displayed reduced electron transport rates (ETR) and chlorophyll a (Chla) content, resulting in reduced cellular POC formation. Interestingly, no differences were observed in non-photochemical quenching (NPQ) or in the ratio of gross photosynthesis to respiration (GP:R). Furthermore, TM quotas were measured, which represent an important and rarely quantified parameter in previous studies. Cellular quotas of manganese, zinc, cobalt and copper remained unchanged while Fe quotas of Fe-deficient cells were reduced by 60% compared with High Fe cells. Based on our data, Fe-deficient Chaetoceros cf. simplex cells were able to efficiently acclimate to low Fe conditions, reducing their intracellular Fe concentrations, the number of functional reaction centers of photosystem II (RCII) and photosynthetic rates, thus avoiding light absorption rather than dissipating the energy through NPQ. Our results demonstrate how Chaetoceros cf. simplex can adapt their physiology to lowered assimilatory metabolism by decreasing respiratory losses.

中文翻译：

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铁限制对南极硅藻 Chaetoceros cf. 碳平衡和光生理学的影响。单纯形

在南大洋 (SO)，铁 (Fe) 限制强烈抑制浮游植物生长并普遍降低其初级生产力。硅藻是碳 (C) 循环的关键组成部分，通过生物碳泵吸收大量人为 CO 2。在这项研究中，我们研究了 Fe 可用性（无 Fe 和 4 nM FeCl 3 添加）对角毛藻生理学的影响。simplex ，一种生态相关的 SO 硅藻。我们的结果是首次将氧气析出和吸收率与颗粒有机碳 (POC) 堆积、色素、光生理参数和缺铁南极硅藻中的细胞内痕量金属 (TM) 配额相结合。氧气释放（通过光合作用，P）和吸收（呼吸，R）的减少与缺铁细胞的生长速率降低相吻合。此外，细胞显示出降低的电子传递率 (ETR) 和叶绿素 a (Chla) 含量，导致细胞 POC 形成减少。有趣的是，在非光化学猝灭 (NPQ) 或总光合作用与呼吸的比率 (GP:R) 中没有观察到差异。此外，还测量了 TM 配额，这在以前的研究中代表了一个重要且很少量化的参数。与高铁电池相比，锰、锌、钴和铜的电池配额保持不变，而缺铁电池的铁配额减少了 60%。根据我们的数据，缺铁角角藻比照。单纯形细胞能够有效地适应低 Fe 条件，降低其细胞内 Fe 浓度、光系统 II (RCII) 功能反应中心的数量和光合速率，从而避免光吸收而不是通过 NPQ 耗散能量。我们的结果证明了角角藻 cf. Simplex 可以通过减少呼吸损失来调整其生理机能以降低同化代谢。