Dissecting, and revealing the controls on, the group-specific CO2 fixation budget of the Atlantic Ocean

海洋在决定世界气候方面发挥着重要作用。这在一定程度上是由于非常小的单细胞光合作用生物--微藻浮游植物--产生氧气和消耗二氧化碳(CO2)。浮游微藻生物量主要由三类组成：原核生物属原氯球菌属和聚球藻属，以及由5微米大小的细胞组成的真核生物。然而，人们对微藻浮游植物“黑箱”内发生的事情知之甚少，特别是关于碳生物量和特定类群初级生产量的分布，这些信息对于理解这些类群在全球碳循环中的作用至关重要。最近，我们的团队优化了放射性示踪剂孵化-流式细胞术分选技术的使用，以揭示北大西洋几个站点的群体特定二氧化碳固定率。除了揭示不同地点之间群体特定二氧化碳固定率的差异外，这些数据还重申了真核生物部分在初级产量估计中的重要性(贡献25%-50%取决于地点)，尽管在数量上它们远远超过了原核生物的对应部分。在这里，我们建议扩展这项工作，以便我们第一次能够揭示在盆地尺度上的群体特定的二氧化碳固定率，以及在地表水和深层叶绿素最大值(DCM)。我们将沿着大西洋子午线横跨英国和福克兰群岛之间的大西洋进行这项工作，并在连续几年进行这项工作，以便i)实现完整的大西洋特定群体的二氧化碳固定预算，ii)可以评估年际变化。此外，我们将使用分类种群的荧光原位杂交和原核生物属(聚球藻和原氯球菌属)的谱系特异性寡核苷酸探针或光合作用微真核生物(PPE)组分的类特异性探针来检验不同分类谱系对微浮游动物群率的准确贡献。因此，该项目将提供二氧化碳原位固定的主要“参与者”和路线的基本信息，这一过程是海洋碳循环的基础。此外，我们将通过营养素添加或照度变化后的机载瓶装实验来研究环境对特定组C固定率的控制。这将使我们了解环境扰动是如何控制特定群体的二氧化碳固定潜力的。我们将把后一项工作与专门针对PPE组分的功能基因组学(转录组学)方法结合起来，以提供控制这一组群的潜在调控因素的补充分子评估。这是基于这样一种想法，即转录图谱将“让生物体告知我们这些生物体正在响应的关键环境参数”。综上所述，这项工作将在我们理解海洋二氧化碳固定的路线和控制方面取得重大进展，这些信息对于预测理解海洋碳循环至关重要。

The oceans play a major role in determining world climate. In part this is due to the production of oxygen and the consumption of carbon dioxide (CO2) by very small, single celled photosynthetic organisms, the picophytoplankton. Picophytoplankton biomass is dominated by three main groups: the prokaryotic genera Prochlorococcus and Synechococcus, and eukaryotes comprising cells <5 micrometres in size. However, little is known of what goes on inside the picophytoplankton 'black box' particularly with respect to the distribution of carbon biomass and group-specific primary production, information which is fundamental to understanding the roles of these groups in the global C cycle. Very recently our team has optimised utilisation of radiotracer incubation-flow cytometric sorting technology, to reveal group-specific CO2 fixation rates at several stations in the North Atlantic. As well as revealing variability in group-specific CO2 fixation rates between sites this data reiterates the importance of the eukaryotic fraction in primary production estimates (contribution 25-50% dependent on location) even though numerically they are vastly outnumbered by their prokaryotic counterparts. Here, we propose to extend this work so that for the first time we can reveal group-specific CO2 fixation rates at the basin scale, as well as in both surface waters and at the deep chlorophyll maximum (DCM). We will perform this work along an Atlantic Meridional Transect, which traverses the Atlantic Ocean between the UK and the Falkland Islands, and in consecutive years, so that i) a complete group-specific CO2 fixation budget of the Atlantic Ocean is attained and ii) inter-annual variability can be assessed. Moreover, we will examine the precise contribution of different taxonomic lineages to the picoplankton group rates using fluorescent in situ hybridisation of sorted populations and lineage-specific oligonucleotide probes for the prokaryotic genera (Synechococcus and Prochlorococcus) or class-specific probes for the photosynthetic picoeukaryote (PPE) fraction. Hence, this project will provide fundamental information of the major 'players' and routes of CO2 fixation in situ, a process that underpins marine C cycling. Furthermore, we will investigate environmental control of group-specific C fixation rates using on-board bottle experiments following either nutrient addition or shifts in irradiance. This will allow us to understand how environmental perturbation controls the CO2 fixation potential of specific groups. We will couple this latter work with a functional genomics (transcriptomics) approach specifically targeted at the PPE fraction to provide a complementary molecular assessment of the potential regulatory factors controlling this group. This is based on the idea that transcriptional profiling will 'let the organism inform us of the key environmental parameters that these organisms are responding to'. Taken together this work will make major inroads in our understanding of the routes and controls of marine CO2 fixation, information which is essential for a predictive understanding of marine C cycling.