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作用有机体，称为硅藻。硅藻作为一群统称为浮游植物的生物的一部分漂浮在海洋表面。全球海洋中分布着成千上万种不同种类的硅藻。一位著名的海洋学家亨利·毕格罗曾经说过：“所有的鱼都是硅藻”，这反映了硅藻作为食物链的基础的重要性，而食物链支撑着世界上最大的渔业。尽管硅藻体型很小，但它们的光合作用每年产生地球上20%的氧气。这比陆地上所有的热带雨林都多。这项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表层海洋携带或输出到深海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的生物，它们的生物碳来自于将溶解在海水中的二氧化碳从大气中转化为有机形式。硅藻还需要一系列由海洋提供的其他营养物质，如氮和磷，对硅藻来说，唯一需要的是用来建造玻璃壳的硅。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上的变化影响了硅藻的属性，比如它们下沉的速度和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，我们最终就可以利用硅藻生理状况和食物网结构的知识来预测硅藻碳进入深海的数量。这项研究涉及在硅藻生理学和基因组学以及海洋化学方面拥有专业知识的研究人员。这项工作最初将与美国宇航局的海洋遥感出口进程(出口)实地计划一起在亚北极北太平洋进行。出口项目正在使用各种各样的方法来量化上层海洋中光合作用固定碳的出口和去向。该研究为本科生、研究生和博士后学者的培养提供了支持。这项研究也将作为针对K-12和初中学生的活动的基础。这项研究将通过形成预测硅藻碳出口的机制基础，广泛影响我们对生物泵(通过光合作用固定的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，硅藻群落的遗传组成、养分使用率和生长反应将被评估，并用硅和铁胁迫的测量来支持，以评估胁迫作为硅藻碳输出路径的预测因子。亚北极北太平洋生态系统的特征是高营养、低叶绿素(HNLC)，这是由于铁(Fe)水平低，铁是限制浮游植物利用其他营养物质的主要控制器。在低铁的HNLC系统中，硅藻在较高的Si：C和Si：N比下生长，并且应该以相对于C显著富含Si的颗粒的形式有效地输出。然而，Fe的限制也改变了硅藻的种类组成，并且低Fe施加的高Si需求可以驱动HNLC区到Si限制或Si/Fe共同限制。因此，HNLC水域中硅和/或铁的压力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链最终改变硅藻碳输出的路径。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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 rainforests 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 photosynthesizers 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 photosynthetically 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 photosynthetically 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.