“鈣板金藻”（又名球石藻，在海洋浮游生物中廣泛分布）在藻類中是獨(dú)特的,，因?yàn)樗鼈儗⑻技扔糜阝}化,、又用于光合作用。在這項(xiàng)研究中,，Clara Bolton和Heather Stoll采用一個(gè)細(xì)胞碳流量模型發(fā)現(xiàn),，當(dāng)二氧化碳濃度低時(shí)，這些生物將會(huì)把碳優(yōu)先分配給光合作用而不是鈣化,，特別是在較大的細(xì)胞中,。這一點(diǎn)反映在小球石和大球石的同位素特征之間的一個(gè)差別上,，該差別在二氧化碳濃度高時(shí)會(huì)減小。這一模式可以在化石記錄中看到,。作者在距今大約600萬年前的小球石和大球石之間發(fā)現(xiàn)了一個(gè)同位素分化,，將此解讀為細(xì)胞的碳獲取對于當(dāng)時(shí)二氧化碳濃度的普遍下降的一種臨界反應(yīng)。（生物谷 Bioon.com）
生物谷推薦的英文摘要
Nature doi:10.1038/nature12448
Late Miocene threshold response of marine algae to carbon dioxide limitation
Clara T. Bolton & Heather M. Stoll
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 era1 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 cultures2, 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 in the atmosphere4, 5, 6. We infer a global decrease in carbon dioxide levels for this time interval that has not yet been identified in the sparse proxy record7 but is synchronous with global cooling and progressive glaciations8, 9.
