Is Carbon Limitation a Driver of Phytoplankton Ecology and Evolution?

我们对海洋和海洋生物如何应对全球气候的巨大变化，如大气中二氧化碳（CO2）浓度增加的理解，主要来自对深海沉积物的研究。随着时间的推移，这些沉积物层层堆积，保存了曾经生活在海洋表面附近的微小单细胞海洋生物-或浮游生物-的化石遗骸。通过钻探这些沉积物，并恢复沉积物的核心和它们所包含的化石，我们可以重建数百万年来海洋条件和生命变化的历史。拟议的项目将研究这些浮游生物群之一-一组称为颗石藻的藻类-它们产生并包围着由方解石（碳酸钙）矿物制成的板状鳞片细胞。颗石藻也可以进行光合作用，利用海水中溶解的碳和光能来制造它们所需的能量和细胞生长的复杂碳分子。像所有的光合生物-包括植物和淡水藻类-颗石藻需要碳作为“资源”，它们在光合作用中使用。它们还需要碳的形式来制造碳酸钙鳞片。根据实验室工作，预计增加海水中溶解碳的量-例如通过增加大气中的CO2浓度-减少了颗石藻细胞如何在光合作用和碳酸钙垢的产生之间分配碳的限制，使细胞生长得更大并产生更大的垢。细胞大小和这些鳞片大小的变化虽然很小，但只有百分之一毫米多一点，如果乘以生活在海洋表面的数十亿个细胞，就会对食物、能源和碳在海洋中的循环产生重大影响。在现代海洋中，要看到碳浓度变化对这类浮游植物的影响还为时过早。然而，来自海洋沉积物的数据保存了数百万年前的颗石藻记录，当时大气中的二氧化碳浓度与未来世纪的预测水平相似。该项目通过测量小细胞和大细胞随时间产生的颗石的化学性质，试图提供迄今为止碳供应限制颗石藻类生长和细胞大小的程度的最详细记录。该项目旨在了解碳的可用性是否是海洋浮游植物生态和进化的主要控制因素，从而对未来世纪海洋浮游植物生态系统可能发生的变化做出更好的预防性预测。

Our understanding of how the oceans and marine life respond to large changes in global climate, such as increased atmospheric carbon dioxide (CO2) concentrations, largely comes from the study of deep ocean sediments. Over time, these sediments build up layer upon layer and preserve the fossil remains of the tiny single celled marine organisms - or plankton - that once lived near the surface of the ocean. By drilling into these sediments, and recovering cores of sedimentary material and the fossils they contain, we can reconstruct a history of changing ocean conditions and life over millions of years. The proposed project will study one of these plankton groups - a group of algae called coccolithophores - that produce and surround their cells in plate-like scales made out of the mineral calcite (calcium carbonate). Coccolithophores can also photosynthesise, using dissolved carbon from sea water together with light energy to make the complex carbon molecules they require for energy and cell growth. Like all photosynthetic organisms - including plants and freshwater algae - the coccolithophores need carbon as a 'resource' which they use during photosynthesis. They also need forms of carbon to make their calcium carbonate scales. From laboratory work, it is expected that increasing the amount of dissolved carbon in sea water - for example by increasing atmospheric CO2 concentrations - reduces the limitations on how coccolithophore cells allocate carbon between photosynthesis and the production of calcium carbonate scales, allowing cells to grow larger and produce larger scales. Changes in cell size and in the size of these scales, although minute, little more than a hundredth of a millimetre in size, when multiplied by the many billions of cells living in the surface ocean can have a significant impact on how food, energy and carbon are cycled through the oceans. In the modern oceans, it's still early to see the effects of changing carbon concentrations on this group of phytoplankton. However, data from ocean sediments preserves a record of the coccolithophores stretching back millions of years, to a time when atmospheric CO2 concentrations were at levels similar to those predicted in the coming century. This project - by measuring the chemistry of coccoliths produced by small and large cells through time - seeks to provide the most detailed record available to date of the degree to which carbon availability limited the growth and cell size of coccolithophore algae. This project seeks to understand if the availability of carbon is a major control on the ecology and evolution of the marine phytoplankton, and so make better precautionary predictions of the likely changes to marine phytoplankton ecosystems in the coming century.