Abstract Coccolithophores are important contributors to global calcium carbonate through their species-specific production of calcite coccoliths. Nannofossil coccolith calcite remains an important tool for paleoreconstructions through geochemical analysis of isotopic and trace element incorporation including Sr, which is a potential indicator of past surface ocean temperature and productivity. Scyphosphaera apsteinii (Zygodiscales) exhibits an unusually high Sr/Ca ratio and correspondingly high partitioning coefficient (DSr = 2.5) in their two morphologically distinct types of coccoliths: flat muroliths and barrel-like lopadoliths. Whether or not this reflects mechanistic differences in calcification compared to other coccolithophores is unknown. We therefore examined the possible role of Sr in S. apsteinii calcification by growing cells in deplete (0.33 mmol/mol Sr/Ca), ambient (9 mmol/mol Sr/Ca), and higher than ambient Sr conditions (36 and 72 mmol/mol Sr/Ca). The effects on growth, quantum efficiency of photosystem II (Fv/Fm), coccolith morphology, and calcite DSr were evaluated. No effect on S. apsteinii growth rate or Fv/Fm was observed when cells were grown in Sr/Ca between 0.33–36 mmol/mol. However, at 72 mmol/mol Sr/Ca growth rate was significantly reduced, although Fv/Fm was unaffected. Reducing the Sr/Ca from ambient (9 mmol/mol) did not significantly alter the frequency of malformed and aberrant muroliths and lopadoliths, but at higher than ambient Sr/Ca conditions coccolith morphology was significantly disrupted. This implies that Sr is not a critical determining factor in normal coccolith calcite morphology in this dimorphic species. Using energy dispersive spectroscopy (EDS) we observed an increase in [Sr] and decrease in DSr of coccoliths as the Sr/Ca of the growth medium increased. Interestingly, muroliths had significantly lower Sr/Ca than lopadoliths at ambient and elevated [Sr], and lopadolith tips had lower Sr than bases in ambient conditions. In summary, the Sr fractionation behavior of S. apsteinii is distinct from other coccolithophores because of an unusually high DSr and inter- and intra-coccolith variability in Sr/Ca. These observations could be explained by mechanistic differences in the selectivity of the Ca2+ transport pathway or in the Sr-and Ca-binding capacity of organic components, such as polysaccharides associated with coccolithogenesis.

中文翻译：

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Scyphosphaera apsteinii 球石中的 Sr：分配行为和在球石形态发生中的作用

摘要 球石藻通过其特定物种的方解石球石生产是全球碳酸钙的重要贡献者。通过对同位素和微量元素掺入（包括 Sr）进行地球化学分析，纳米化石颗石方解石仍然是古重建的重要工具，Sr 是过去海洋表面温度和生产力的潜在指标。Scyphosphaera apsteinii (Zygodiscales) 表现出异常高的 Sr/Ca 比率和相应的高分配系数 (DSr = 2.5) 在其两种形态不同的球石类型：扁平的石块和桶状的石块。与其他颗石藻相比，这是否反映了钙化的机制差异尚不清楚。因此，我们研究了 Sr 在 S 中的可能作用。通过在耗尽 (0.33 mmol/mol Sr/Ca)、环境 (9 mmol/mol Sr/Ca) 和高于环境 Sr 条件（36 和 72 mmol/mol Sr/Ca）的条件下生长细胞，apsteinii 钙化。评估了对光系统 II (Fv/Fm) 的生长、量子效率、球石形态和方解石 DSr 的影响。当细胞在 0.33–36 mmol/mol 的 Sr/Ca 中生长时，没有观察到对 S. apsteinii 生长速率或 Fv/Fm 的影响。然而，在 72 mmol/mol Sr/Ca 生长速率显着降低，尽管 Fv/Fm 不受影响。从环境 (9 mmol/mol) 中减少 Sr/Ca 并没有显着改变畸形和异常的壁石和 lopadoliths 的频率，但在高于环境 Sr/Ca 的条件下，球石形态被显着破坏。这意味着 Sr 不是这种双相物种中正常颗石方解石形态的关键决定因素。使用能量色散光谱 (EDS)，我们观察到随着生长培养基中 Sr/Ca 的增加，[Sr] 的增加和颗石的 DSr 减少。有趣的是，在环境和升高的 [Sr] 下，壁石的 Sr/Ca 显着低于 lopadoliths，并且 lopadolith 尖端的 Sr 低于环境条件下的基地。总之，S. apsteinii 的 Sr 分馏行为与其他颗石藻不同，因为 Sr/Ca 的 DSr 异常高以及颗石内和颗石内的变异性。这些观察结果可以通过 Ca2+ 转运途径的选择性或有机成分的 Sr 和 Ca 结合能力的机械差异来解释，