Late Miocene threshold response of marine algae to carbon dioxide limitation
Late Miocene threshold response of marine algae to carbon dioxide limitation
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DOI：
10.1038/nature12448
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发表时间：
2013-08-29
期刊：
影响因子：
64.8
通讯作者：
Stoll, Heather M.
中科院分区：
文献类型：
--
作者：
Bolton, Clara T.;Stoll, Heather M.
颗石藻是利用碳进行钙化和光合作用的海藻。这些和其他海洋藻类在新生代（1）期间对二氧化碳水平降低的长期适应导致现代藻类能够在光合作用部位积极增加二氧化碳。这种增强通过溶解的碳酸氢盐（HCO 3-）的运输和酶的帮助发生，这些酶的表达可以通过实验室培养物中可变的含水二氧化碳浓度[CO2]进行调节（2，3）。颗石藻保存了这种适应的地质历史，因为它们的方解石板（颗石藻）的稳定碳和氧同位素组成，保存在化石记录中，对细胞吸收和运输活性碳很敏感。在这里，我们使用一个模型的细胞碳通量，并表明，在低[CO2]的HCO 3-在光合作用的网站上的需求增加的结果在减少分配的HCO 3-钙化，这是最明显的较大的细胞。这导致在一个大的分歧之间的碳同位素组成的小与大cocoliths只有在低[CO2]。我们的氧和碳同位素记录的大小分离的化石球石的评估表明，这种同位素分歧首次出现在晚中新世最早上新世时代（约7-5百万年前）。我们将其解释为细胞的碳获取策略对减少[CO2]的阈值响应。记录的颗石藻响应与800万年至500万年前陆地植被分布的全球变化同步，一些研究将其解释为植物对大气中二氧化碳分压（p（CO2））降低的响应（4-6）。我们推断，在这段时间间隔内，全球二氧化碳水平下降，这在稀疏的p（CO2）代用记录中尚未发现（7），但与全球变冷和渐进冰川同步（8，9）。
Coccolithophores are marine algae that use carbon for calcification and photosynthesis. The long-term adaptation of these and other marine algae to decreasing carbon dioxide levels during the Cenozoic era(1) has resulted in modern algae capable of actively enhancing carbon dioxide at the site of photosynthesis. This enhancement occurs through the transport of dissolved bicarbonate (HCO3-) and with the help of enzymes whose expression can be modulated by variable aqueous carbon dioxide concentration, [CO2], in laboratory cultures(2,3). Coccolithophores preserve the geological history of this adaptation because the stable carbon and oxygen isotopic compositions of their calcite plates (coccoliths), which are preserved in the fossil record, are sensitive to active carbon uptake and transport by the cell. Here we use a model of cellular carbon fluxes and show that at low [CO2] the increased demand for HCO3- at the site of photosynthesis results in a diminished allocation of HCO3- to calcification, which is most pronounced in larger cells. This results in a large divergence between the carbon isotopic compositions of small versus large coccoliths only at low [CO2]. Our evaluation of the oxygen and carbon isotope record of size-separated fossil coccoliths reveals that this isotopic divergence first arose during the late Miocene to the earliest Pliocene epoch (about 7-5 million years ago). We interpret this to be a threshold response of the cells' carbon acquisition strategies to decreasing [CO2]. The documented coccolithophore response is synchronous with a global shift in terrestrial vegetation distribution between 8 and 5 Myr ago, which has been interpreted by some studies as a floral response to decreasing partial pressures of carbon dioxide (p(CO2)) in the atmosphere(4-6). We infer a global decrease in carbon dioxide levels for this time interval that has not yet been identified in the sparse p(CO2) proxy record(7) but is synchronous with global cooling and progressive glaciations(8,9).