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

合作研究：高CO2海洋中的铁生物利用率：硅藻中铁获取机制的新观点铁是所有海洋浮游植物生长所必需的，海洋食物链基础上的微观植物。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。预计OA会通过降低碳酸根离子的浓度来影响海水化学。浮游植物从环境中吸收铁需要碳酸根离子，这表明OA可能抑制铁营养。使情况进一步复杂化的是，pH值的变化会影响海水中的铁化学，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OA引起的海洋化学变化将如何影响浮游植物对铁的利用率知之甚少。浮游植物铁吸收和相关生长速率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关键化学元素（如碳和氮）及其化学性质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社区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微生物学、地球化学循环和当前全球变化专题方面的教育推广活动。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），斯克里普斯桦树水族馆（BAS）和海洋发现研究所（ODI）。该项目旨在了解硅藻铁收购策略对海水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械理解将有助于大大提高预测海洋pH值和无机碳化学变化对硅藻铁吸收率的影响的能力。这一关键的地球化学问题是通过痕量金属清洁操作实验，结合国家的最先进的分析方法来探讨浮游植物细胞生理学和地球化学实验室培养和自然社区。在第一年，实验室实验与模式羽纹硅藻利用一系列有针对性的基因敲除转基因株系，以评估不同的铁同化途径的底物特异性和相对重要性的范围内的pCO 2和铁的可用性条件。此外，在南加州海流的自然群落中，对关键硅藻铁同化途径的mRNA和蛋白质进行定量，进一步阐明了不同铁同化途径与pCO 2和铁可用性相关的相对重要性和敏感性。在第二年的拉格朗日铁的吸收率和相关的mRNA和蛋白质丰度的研究进行上涌高pCO 2水在海上平流的过程中。此外，研究人员正在使用自然升高的高pCO 2海水进行中生态系统实验，以及对多重敲除线进行实验室实验。 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精确概念模型，随后利用该模型描述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，和量化的相对贡献不同的铁收购途径在高pCO 2浮游植物群落。

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.