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

合作研究：高二氧化碳海洋中铁的生物可利用性：硅藻中铁获取机制的新视角铁对于所有海洋浮游植物的生长至关重要，浮游植物是海洋食物链底部的微型植物。因此，全球海洋大片区域缺铁限制了浮游植物的生长和商业渔业。海洋酸化是由于海洋吸收大气中的二氧化碳而导致的海水pH值的持续下降。据预测，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才能从环境中吸收铁，这表明OA可能会抑制铁的营养。使情况更加复杂的是，pH的变化会影响海水中的铁的化学成分，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，人们对海洋化学成分的变化将如何影响浮游植物对铁的利用知之甚少。浮游植物铁吸收和相关生长速度的变化可能会对海洋捕获大气二氧化碳(CO2)的方式产生重大影响。这对生态系统生产力和碳、氮等关键化学元素及其化学的全球循环具有重要影响。该项目旨在帮助我们了解海水pH值和溶解无机碳的化学变化将如何影响实验室和自然社区的铁摄取率和铁获取策略。该项目还包括开展以小学生为对象的微生物学、生物地球化学循环和当前全球变化专题方面的教育宣传活动。这些科学推广活动得益于与圣地亚哥的以下组织的合作：非凡科学家和工程师联盟(LXS)、斯克里普斯白桦水族馆(BAS)和海洋发现研究所(ODI)。该项目试图了解硅藻铁获取策略对海水pH值和碳酸盐化学变化的不同敏感性。最终，对硅藻铁吸收途径的更彻底和更详细的机制了解将有助于大大提高预测海洋pH和无机碳化学预期变化对硅藻铁吸收速率的影响的能力。这一关键的生物地球化学问题是通过结合最先进的分析方法的痕量金属清洁操作实验来解决的，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。在第一年，实验室对一种模式羽叶状硅藻进行了实验，利用一组定向敲除转基因株系来评估不同的铁同化途径在一系列二氧化碳和铁可利用性条件下的底物专一性和相对重要性。此外，对南加州当前自然群落中关键的硅藻铁同化途径的mRNA和蛋白质的定量研究进一步阐明了不同的铁同化途径相对于二氧化碳和铁有效性的相对重要性和敏感性。在第二年，拉格朗日研究了在近海平流过程中上升的高二氧化碳分压水的铁吸收速率和相关的信使核糖核酸和蛋白质丰度。此外，研究人员正在使用自然升高的高二氧化碳海水进行中生体实验，以及在多重淘汰线上进行实验室实验。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吸收的改进概念模型，并随后利用该模型来表征不同铁吸收途径对海洋酸化影响的敏感性；2)确定酸化对铁吸收的影响，并量化高二氧化碳浮游植物群落中不同铁吸收途径的相对贡献。

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.