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

该项目的重点是南大洋（SO）中的一组重要的光合藻类，硅藻，以及相关的细菌群落在调节其生长中所起的作用。硅藻的生长为SO食物网提供燃料，并通过在细胞下沉到表面以下的长时间尺度上将用于生长的碳隔离到深海来平衡大气中的二氧化碳。硅藻的生长受到海水中可利用的铁的限制，其中大部分铁不能自由地被硅藻利用，而是与其他化合物紧密结合。这些化合物的性质以及浮游植物如何从中获得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，以描述硅藻，其相关细菌和铁之间的关系，在开放的海洋和近海沃茨。实验将涉及以不同的营养物质比例向天然浮游植物组合提供营养物质，以确定硅藻及其相关细菌对不同条件的反应。这将为气候和食物网建模者提供有价值的数据，并将帮助我们更好地了解铁（海洋中的一种关键营养素）与食物网基础生物之间的关系，这些生物利用铁进行光合作用生长和碳吸收。该项目还将进一步推动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员和研究生和本科生的培训，以及与罗得岛中学女童子军，弗吉尼亚州内城初中和高中年龄女孩以及佛罗里达中学女孩的外展活动。该项目结合了痕量金属地球化学，浮游植物培养，和分子生物学，以解决有关铁结合化合物的生产和细菌的相互作用，在这个铁有限的区域的作用的问题。铁是海洋浮游植物必需的微量营养元素。浮游植物生长的SO是有限的，缺乏足够的铁，在这个高纬度地区的碳循环和气候的重要后果。铁地球化学中的一些主要悬而未决的问题涉及到有机化合物，这些有机化合物结合了海洋表面99.9%的溶解铁。研究人员先前在这一地区的研究表明，SO中强铁结合化合物的产生与硝酸盐与铁比率高的沃茨中的硅藻水华有关。这些化合物的来源尚不清楚，但研究人员假设它们可能来自细菌，已知细菌会产生这些化合物供自己使用。该项目将测试三个假设，这些铁结合化合物的生产，铁的生物可用性的限制，即使在高浓度存在，以及在这些过程中的作用与细菌相关。该项目的结果将提供有关SO中天然强铁结合化合物生产的生物地球化学触发因素、生物来源和功能的基本信息，其中铁在浮游植物生产力、碳循环和气候调节中起着关键作用。

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.