Collaborative Research: Iron Bioavailability in High-CO2 Oceans: New Perspectives on Iron Acquisition Mechanisms in Diatoms

高二氧化碳海洋中的铁生物利用度：硅藻铁获取机制的新视角铁对于所有海洋浮游植物（海洋食物链底部的微观植物）的生长都是至关重要的。因此，全球海洋大部分地区缺铁限制了浮游植物的生长和商业渔业。海洋酸化（OA）是由于海洋从大气中吸收二氧化碳而导致海水pH值持续下降的现象。预计OA会通过降低碳酸盐离子的浓度来影响海水化学。浮游植物需要碳酸盐离子从其环境中吸收铁，这表明OA可能抑制铁营养。更复杂的是，pH值的变化会影响海水中的铁化学成分，因此预计OA会改变各种形式铁的相对丰度。但是，尽管有这些期望，由于OA引起的海洋化学变化将如何影响浮游植物对铁的可用性，人们知之甚少。浮游植物对铁的吸收和相关生长率的变化可能会对海洋如何捕获大气中的二氧化碳（CO2）产生重大影响。这对生态系统生产力和关键化学元素（如碳和氮）的全球循环及其化学性质具有重要影响。该项目旨在帮助我们了解海水pH值的变化和溶解无机碳的化学性质将如何影响实验室和自然群落中的铁吸收率和铁获取策略。该项目还包括开展针对小学生的教育外展活动，内容涉及微生物学、生物地球化学循环和当前全球变化主题。这些科学推广活动得益于与以下圣地亚哥组织的合作：杰出科学家和工程师联盟（LXS），斯克里普斯的伯奇水族馆（BAS）和海洋发现研究所（ODI）。该项目旨在了解硅藻铁获取策略对海水pH值和碳酸盐化学变化的差异敏感性。最终，对硅藻铁吸收途径的更彻底和详细的机制理解将有助于大大提高预测海洋pH和无机碳化学变化对硅藻铁吸收速率的影响的能力。这个关键的生物地球化学问题是通过微量金属清洁操作实验来解决的，该实验结合了最先进的分析方法，以探索实验室培养和自然群落中的浮游植物细胞生理学和生物地球化学。第一年，我们利用一种pennate硅藻模型进行了实验室实验，利用一系列靶向敲除转基因系来评估在一系列二氧化碳分压和铁可用性条件下，不同铁同化途径的底物特异性和相对重要性。此外，对南加州洋流自然群落中关键硅藻铁同化途径的mRNA和蛋白质的定量分析进一步阐明了不同铁同化途径与二氧化碳分压和铁有效性相关的相对重要性和敏感性。在第二年，在近海平流过程中，对上涌的高二氧化碳分压水进行了铁摄取率和相关mRNA和蛋白质丰度的拉格朗日研究。此外，研究人员正在使用自然升高的高pCO2海水进行中生态实验，并对多重敲除系进行实验室实验。第三年致力于数据分析和整体项目综合。研究活动的总体目标包括：1)开发和验证关键海洋浮游植物铁摄取的精炼概念模型，并随后利用该模型表征不同铁摄取途径对海洋酸化影响的敏感性；2)确定酸化对铁摄取的影响，并量化高二氧化碳分压浮游植物群落中不同铁获取途径的相对贡献。

Collaborative Research: Iron Bioavailability in High-CO2 Oceans: New Perspectives on Iron Acquisition Mechanisms in DiatomsIron is critically needed for growth of all marine phytoplankton, the microscopic plants at the base of the ocean food chain. Consequently, lack of iron in large regions of the global ocean limits phytoplankton growth and commercial fisheries. Ocean acidification (OA) is the ongoing decrease in seawater pH due to the ocean absorbing carbon dioxide from the atmosphere. OA is predicted to affect seawater chemistry by reducing the concentration of carbonate ions. Carbonate ions are required for phytoplankton to take up iron from their environment, which suggests that OA might inhibit iron nutrition. Further complicating the scenario, pH changes affect iron chemistry in seawater, such that OA is predicted to shift the relative abundance of various forms of iron. But despite these expectations, little is known about how the changes in ocean chemistry due to OA will impact the availability of iron to phytoplankton. Changes in phytoplankton iron uptake and associated growth rates would likely have large effects on how the ocean captures atmospheric carbon dioxide (CO2). This has important consequences for ecosystem productivity and for global cycles of critical chemical elements, such as carbon and nitrogen, and their chemistry. This project aims to help us understand how shifts in seawater pH and the chemistry of dissolved inorganic carbon will affect both iron uptake rates and iron acquisition strategies in the laboratory and in natural communities. This project also includes development of educational outreach activities which target primary school students in the areas of microbiology, biogeochemical cycles and current global change topics. These science outreach activities benefit from collaborations with the following San Diego-based organizations: the League of Extraordinary Scientists and Engineers (LXS), The Birch Aquarium at Scripps (BAS), and The Ocean Discovery Institute (ODI).This project seeks to understand the differential sensitivity of diatom iron acquisition strategies to changes in seawater pH and carbonate chemistry. Ultimately a more thorough and detailed mechanistic understanding of diatom iron uptake pathways will facilitate a much-improved ability to forecast the impact of anticipated changes in ocean pH and inorganic carbon chemistry on rates of iron uptake by diatoms. This critical biogeochemical issue is addressed through trace metal clean manipulation experiments incorporating state-of-the-art analytical methodology to probe phytoplankton cellular physiology and biogeochemistry in laboratory cultures and natural communities. In the first year, laboratory experiments with a model pennate diatom leverage a collection of targeted knockout transgenic lines to evaluate the substrate specificity and relative importance of distinct iron assimilation pathways under a range of pCO2 and iron availability conditions. Additionally, quantitation of mRNA and proteins for key diatom iron assimilation pathways in natural communities in the Southern California Current further clarify the relative importance and sensitivity of distinct iron assimilation pathways in relation to pCO2 and iron availability. In year two a Lagrangian study of iron uptake rates and associated mRNA and protein abundance is performed on upwelled high pCO2 water over the course of offshore advection. Additionally, the investigators are conducting mesocosm experiments using naturally elevated high pCO2 seawater as well as laboratory experiments on multiplex knockout lines. Year three is dedicated to data analyses and overall project synthesis. Overall aims of the research activities include, 1) development and validation of a refined conceptual model of iron uptake in key marine phytoplankton and subsequent utilization of the model to characterize the sensitivity of distinct iron uptake pathways to the effects of ocean acidification, and 2) determination of the effects of acidification on iron uptake, and quantification of the relative contribution of distinct iron acquisition pathways in high pCO2 phytoplankton communities.