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

本项目主要研究南大洋（SO）中一种重要的光合藻类硅藻，以及相关细菌群落在调节其生长过程中所起的作用。硅藻的生长为SO食物网提供燃料，并通过将用于生长的碳在长时间尺度上隔离到深海，从而平衡大气中的二氧化碳，因为细胞下沉到海面以下。硅藻的生长受到海水中可用铁的限制，其中大部分铁不是硅藻可以自由获得的，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，以确定开阔海域和近海水域中硅藻及其相关细菌与铁之间的关系。实验将包括向天然浮游植物组合提供不同营养比例的营养物，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，它将帮助我们更好地理解铁（海洋中的一种关键营养物质）与食物网底部利用铁进行光合作用生长和碳吸收的生物之间的关系。该项目还将进一步实现国家科学基金会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，以及与罗德岛州的中学女童子军、弗吉尼亚州内城的初中和高中女生以及佛罗里达州的初中女生的外展活动。该项目结合了痕量金属生物地球化学、浮游植物培养和分子生物学，以解决有关铁结合化合物的产生以及硅藻-细菌在铁限制区域相互作用的问题。铁是海洋浮游植物必需的微量营养素。由于缺乏足够的铁，浮游植物在SO中的生长受到限制，这对高纬度地区的碳循环和气候产生了重要影响。铁生物地球化学中一些悬而未决的主要问题与有机化合物有关，这些有机化合物结合了海洋表面99.9%的溶解铁。研究人员先前在该地区的研究表明，SO中强铁结合化合物的产生与硝酸盐与铁的高比例水体中的硅藻繁殖有关。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，因为已知细菌会产生这些化合物以供自己使用。该项目将测试关于这些铁结合化合物的生产的三个假设，铁的生物可用性的限制，即使高浓度存在，以及硅藻相关细菌在这些过程中的作用。该项目的研究结果将为研究SO中天然强铁结合化合物的生物地球化学触发机制、生物来源和功能提供基础信息，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.