During the Mesozoic Era, dinoflagellates, coccolithophorids and diatoms became prominent primary producers in the oceans, succeeding an earlier biota in which green algae and cyanobacteria had been proportionally more abundant. This transition occurred during an interval marked by increased sulfate concentration in seawater. To test whether increasing sulfate availability facilitated the evolutionary transition in marine phytoplankton, the cyanobacterium Synechococcus sp., the green alga Tetraselmis suecica and three algae containing chlorophyll a+c (the diatom Thalassiosira weissflogii, the dinoflagellate Protoceratium reticulatum and the coccolithophorid Emiliania huxleyi) were grown in media containing 1, 5, 10, 20, or 30 mm SO₄²⁻. The cyanobacterium and the green alga showed no growth response to varying [SO₄²⁻]. By contrast, the three chlorophyll a+c algae showed improved growth with higher [SO₄²⁻], but only up to 10 mm. The chlorophyll a+c algae, but not the green alga or cyanobacterium, also showed lower C:S with higher [SO₄²⁻]. When the same experiment was repeated in the presence of a ciliate predator (Euplotes sp.), T. suecica and T. weissflogii increased their specific growth rate in most treatments, whereas the growth rate of Synechococcus sp. was not affected or decreased in the presence of grazers. In a third experiment, T. suecica, T. weissflogii, P. reticulatum and Synechococcus sp. were grown in conditions approximating modern, earlier Paleozoic and Proterozoic seawater. In these treatments, sulfate availability, nitrogen source, metal availability and Pco₂ varied. Monospecific cultures exhibited their highest growth rates in the Proterozoic treatment. In mixed culture, T. weissflogii outgrew other species in modern seawater and T. suecica outgrew the others in Paleozoic water. Synechococcus sp. grew best in Proterozoic seawater, but did not outgrow eukaryotic species in any treatment. Collectively, our results suggest that secular increase in seawater [SO₄²⁻] may have facilitated the evolutionary expansion of chlorophyll a+c phytoplankton, but probably not to the exclusion of other biological and environmental factors.

中文翻译：

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硫酸盐的可用性是否促进了海洋中叶绿素a + c浮游植物的进化扩张？

在中生代时期，单鞭毛纲，球藻类和硅藻类成为海洋中主要的主要生产者，接替了较早的生物群落，在该生物群落中，绿藻和蓝细菌比例成比例地增加。这种过渡发生在海水中硫酸盐浓度升高的时间间隔内。为了测试硫酸盐可用性的增加是否促进了海洋浮游植物，蓝藻Synechococcus sp。，绿藻Tetraselmis suecica和三种含叶绿素a + c的藻类（硅藻Thalassiosira weissflogii，硅藻鞭毛原藻和球藻鞘藻）的进化过渡，Emiliania huxleyi）在含有1、5、10、20或30 m m SO ₄ ^2-的培养基中生长。蓝藻和绿藻对[SO ₄ ^2- ]的变化无生长反应。相比之下，三种叶绿素a + c藻类在[SO ₄ ^2- ]较高的情况下显示出改善的生长，但最高可达10 m m。叶绿素a + c藻类（但不是绿藻或蓝藻）也显示出较低的C：S和较高的[SO ₄ ^2- ]。在有纤毛捕食者（Euplotes sp。）的情况下重复相同的实验时，T. suecica和T. weissflogii在大多数的治疗增加了他们的特定生长率，而增速聚球藻。在有放牧者的情况下不会受到影响或减少。在第三个实验，T. suecica，T. weissflogii，P.网藻和聚球藻。在接近现代，较早的古生代和元古代的海水条件下生长。在这些处理中，硫酸盐的利用率，氮源，金属的利用率和P co _2均不同。单特异性培养物在元古代治疗中表现出最高的生长速度。在混合文化中，T。weissflogii在现代海水中，其他物种的数量超过了其他物种；在古生代水中，T。suecica的物种数量超过了其他物种。粘球菌 在元古代海水中生长最快，但在任何处理中都没有超过真核生物。总体而言，我们的结果表明，海水[SO ₄ ^2- ]的长期增加可能促进了叶绿素a + c浮游植物的进化扩展，但可能并未排除其他生物和环境因素。