Collaborative Research: Investigating Iron-inding Ligands in Southern Ocean Diatom Communities: The Role of Diatom-Bacteria Associations

该项目重点研究了南大洋中一种重要的光合作用藻类--硅藻，以及相关细菌群落在调节其生长中所起的作用。硅藻的生长为SO食物链提供燃料，并通过将用于生长的碳在长时间尺度上隔离到深海中来平衡大气中的二氧化碳，因为细胞下沉到表面以下。硅藻的生长受到海水中有效铁的限制，其中大部分铁不是硅藻自由获得的，而是与其他化合物紧密结合在一起的。这些化合物的性质以及浮游植物如何从这些化合物中获取铁，对于了解该地区和全球的生产力至关重要。研究人员将进行实验，以确定硅藻及其伴生细菌与公海和近岸水域中的铁之间的关系。实验将涉及向自然浮游植物组合提供不同营养比例的营养物质，以确定硅藻及其相关细菌如何对不同条件做出反应。这将提供有价值的数据，可供气候和食物网络建模人员使用，它将帮助我们更好地理解海洋中的关键营养物质铁与食物网络底部的生物之间的关系，这些生物利用铁进行光合作用生长和碳吸收。该项目还将推动NSF培养新一代科学家和向公众提供科学发现的目标。该项目支持早期职业高级调查人员和研究生和本科生的培训，以及与罗德岛州的中学女童子军、弗吉尼亚州市中心的初中和高中年龄女孩以及佛罗里达州的中学女孩的外联活动。该项目结合痕量金属生物地球化学、浮游植物培养和分子生物学来解决有关铁结合化合物的生产和硅藻-细菌相互作用在这个铁有限的地区的作用的问题。铁是海洋浮游植物必需的微量营养素。由于缺乏足够的铁，SO中浮游植物的生长受到限制，对这一高纬度地区的碳循环和气候产生了重要影响。铁生物地球化学中的一些主要悬而未决的问题与有机化合物有关，这些有机化合物结合了表层海洋中99.9%的溶解铁。研究人员先前在该地区的研究表明，SO中强铁结合化合物的产生与高硝酸盐与铁比例的水域中的硅藻水华有关。这些化合物的来源尚不清楚，但研究人员推测，它们可能来自细菌，众所周知，细菌会产生此类化合物供自己使用。该项目将测试关于这些铁结合化合物的生产、即使存在高浓度铁的生物可获得性的限制以及硅藻相关细菌在这些过程中的作用的三个假说。该项目的结果将提供有关SO中天然强铁结合化合物产生的生物地球化学触发因素、生物来源和功能的基本信息，在SO中，铁在浮游植物生产力、碳循环和气候调节中发挥关键作用。

This project focuses on an important group of photosynthetic algae in the Southern Ocean (SO), diatoms, and the roles associated bacterial communities play in modulating their growth. Diatom growth fuels the SO food web and balances atmospheric carbon dioxide by sequestering the carbon used for growth to the deep ocean on long time scales as cells sink below the surface. The diatom growth is limited by the available iron in the seawater, most of which is not freely available to the diatoms but instead is tightly bound to other compounds. The nature of these compounds and how phytoplankton acquire iron from them is critical to understanding productivity in this region and globally. The investigators will conduct experiments to characterize the relationship between diatoms, their associated bacteria, and iron in open ocean and inshore waters. Experiments will involve supplying nutrients at varying nutrient ratios to natural phytoplankton assemblages to determine how diatoms and their associated bacteria respond to different conditions. This will provide valuable data that can be used by climate and food web modelers and it will help us better understand the relationship between iron, a key nutrient in the ocean, and the organisms at the base of the food web that use iron for photosynthetic growth and carbon uptake. The project will also further the NSF goals of training new generations of scientists and of making scientific discoveries available to the general public. The project supports early career senior investigators and the training of graduate and undergraduate students as well as outreach activities with middle school Girl Scouts in Rhode Island, inner city middle and high school age girls in Virginia, and middle school girls in Florida.The project combines trace metal biogeochemistry, phytoplankton cultivation, and molecular biology to address questions regarding the production of iron-binding compounds and the role of diatom-bacterial interactions in this iron-limited region. Iron is an essential micronutrient for marine phytoplankton. Phytoplankton growth in the SO is limited by a lack of sufficient iron, with important consequences for carbon cycling and climate in this high latitude regime. Some of the major outstanding questions in iron biogeochemistry relate to the organic compounds that bind 99.9% of dissolved iron in surface oceans. The investigators' prior research in this region suggests that production of strong iron-binding compounds in the SO is linked to diatom blooms in waters with high nitrate to iron ratios. The sources of these compounds are unknown but the investigators hypothesize that they may be from bacteria, which are known to produce such compounds for their own use. The project will test three hypotheses concerning the production of these iron-binding compounds, limitations on the biological availability of iron even if present in high concentrations, and the roles of diatom-associated bacteria in these processes. Results from this project will provide fundamental information about the biogeochemical trigger, and biological sources and function, of natural strong iron-binding compound production in the SO, where iron plays a critical role in phytoplankton productivity, carbon cycling, and climate regulation.