Collaborative Research: Diatoms, Food Webs and Carbon Export - Leveraging NASA EXPORTS to Test the Role of Diatom Physiology in the Biological Carbon Pump

这个项目的重点是海洋中一组微小的单细胞光合生物，叫做硅藻。硅藻作为一组统称为浮游植物的生物的一部分漂浮在海洋表面。有成千上万种不同种类的硅藻分布在全球海洋中。著名海洋学家亨利·毕格罗曾说过：“所有的鱼都是硅藻”，这反映了硅藻作为食物链基础的重要性，硅藻支撑着世界上最大的渔业。尽管体型很小，但硅藻光合作用每年产生的氧气占地球上氧气总量的20%。这比陆地上所有的热带雨林还要多。该研究的主要目的是了解硅藻物种之间的代谢差异如何影响从海洋表层到深海携带或出口的硅藻有机碳的数量。由于硅藻和绿色植物一样是光合作用者，它们的生物碳来自于将大气中溶解在海水中的二氧化碳转化为有机形式。硅藻还需要海洋提供的一系列其他营养物质，如氮和磷，以及硅藻特有的用于构建其玻璃壳的硅。这项研究将调查硅藻之间的遗传和生理差异如何影响每个物种对海洋营养水平变化的反应，以及这些变化如何影响硅藻碳向深海的出口。硅藻的生理反应和它们的碳输出之间的联系是因为生理变化会影响硅藻的属性，比如它们下沉的速度和它们对捕食者的美味程度。因此，如果我们能够将不同硅藻的生理状况与不同物种遵循的食物网途径联系起来，我们最终可以利用硅藻生理状态和食物网结构的知识来预测有多少硅藻碳进入深海。这项研究涉及具有硅藻生理学和基因组学以及海洋化学专业知识的研究人员。这项工作最初将在北太平洋亚北极地区进行，与NASA海洋遥感出口过程（EXPORTS）领域计划一起进行。“出口”计划使用多种方法量化上层海洋光合作用固定碳的出口和归宿。该研究支持本科生、研究生和一名博士后的培养。该研究还将作为针对K-12和初中学生的活动的基础。该研究将通过形成预测硅藻碳输出的机制基础，广泛影响我们对生物泵（光合作用固定有机碳向深海的运输）生物学的理解。假设硅藻生理胁迫的类型和程度是驱动出口的生态系统状态的重要方面。为了验证这一假设，我们将对硅藻群落的遗传组成、养分利用速率和生长响应进行评估，并通过硅和铁胁迫测量来支持，以评估胁迫对硅藻碳输出路径的预测作用。北太平洋亚北极生态系统的特点是高营养低叶绿素（HNLC），因为低铁（Fe）水平是限制浮游植物利用其他营养物质的主要控制因素。硅藻生长在高Si:C和Si:N比例的低铁HNLC系统中是一个范例，并且应该作为相对于C显著富集Si的颗粒有效地出口。然而，铁限制也改变了硅藻的物种组成，低铁所施加的高Si需求可以驱动HNLC区域达到Si限制或Si/Fe共限制。因此，高低温水体中硅和/或铁的胁迫程度都可以改变硅藻的分类组成、硅藻细胞的元素组成以及细胞通过食物网的路径，最终改变硅藻碳的输出。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This project focuses on a group of microscopic single-celled photosynthetic organisms in the ocean called diatoms. Diatoms float in the surface ocean as part of a group of organisms collectively called phytoplankton. There are thousands of different species of diatoms distributed across the global ocean. A famous oceanographer Henry Bigelow once said "All fish is diatoms" reflecting the importance of diatoms as the base of the food chain that supports the world's largest fisheries. Despite their small size, diatom photosynthesis produces 20% of the oxygen on earth each year. That's more than all of the tropical rain forests on land. The major objective of the research is to understand how the metabolic differences among diatom species affects the amount of diatom organic carbon that is carried, or exported, from the surface ocean to the deep ocean. As diatoms are photo-synthesizers like green plants, their biological carbon comes from converting carbon dioxide dissolved in seawater from the atmosphere into organic forms. Diatoms also require a series of other nurtrients supplied by the ocean such as nitrogen and phosphorous and, uniquely for diatoms, the silicon used to construct their glass shells. This research will investigate how genetic and physiological differences among diatoms influence how each species react to changes in nutrient levels in the ocean and how those shifts affect the export of diatom carbon to the deep sea. The link between diatoms' physiological response and their carbon export comes about because shifts in physiology affect diatom attributes like how fast they sink and how tasty they are to predators. So if we can relate the physiological condition of different diatoms to the food-web pathways followed by different species, we can ultimately use knowledge of diatom physiological status and food web structure to predict how much diatom carbon gets to the deep sea. The research involves investigators with expertise in the physiology and genomics of diatoms and in the ocean's chemistry. The work will initially take place in the subarctic North Pacific in conjunction with the NASA Export Processes in the Ocean from RemoTe Sensing (EXPORTS) field program. The EXPORTS program is using a wide variety of methods to quantify the export and fate of photo-synthetically fixed carbon in the upper ocean. The research supports the training of undergraduate students, graduate students and a postdoctoral scholar. The research will also serve as the basis for activities aimed at K-12 and junior high school students. The research will broadly impact our understanding of the biology of the biological pump (the transport of photo-synthetically fixed organic carbon to the deep sea) by forming a mechanistic basis for predicting the export of diatom carbon. It is hypothesized that the type and degree of diatom physiological stress are vital aspects of ecosystem state that drive export. To test this hypothesis, the genetic composition, rates of nutrient use and growth response of diatom communities will be evaluated and supported with measurements of silicon and iron stress to evaluate stress as a predictor of the path of diatom carbon export. The subarctic N. Pacific ecosystem is characterized as high nutrient low chlorophyll (HNLC) due to low iron (Fe) levels that are primary controllers constraining phytoplankton utilization of other nutrients. It has been a paradigm in low Fe, HNLC systems that diatoms grow at elevated Si:C and Si:N ratios and should be efficiently exported as particles significantly enriched in Si relative to C. However, Fe limitation also alters diatoms species composition and the high Si demand imposed by low Fe can drive HNLC regions to Si limitation or Si/Fe co-limitation. Thus, the degree of Si and/or Fe stress in HNLC waters can all alter diatom taxonomic composition, the elemental composition of diatom cells, and the path cells follow through the food web ultimately altering diatom carbon export.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.