Mechanisms controlling the production and fate of DOM during diatom blooms

硅藻华期 DOM 产生和命运的控制机制

• 批准号: 0850857
• 负责人: Craig Carlson
• 金额: $ 68.96万
• 依托单位: University of California-Santa Barbara
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-04-01 至 2014-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0850857&HistoricalAwards=false
• 关键词: Mechanisms; controlling; production; fate; DOM

Intellectual Merit: The residence time of DOM in surface waters of marine systems is the main factor determining its contribution to the efficiency and magnitude of the biological carbon pump. There is growing evidence that the export of DOM from the surface ocean represents a highly efficient pathway for the sequestration of organic carbon in the deep sea in some ocean regions. Current estimates are that 20% of the carbon transported to depth by the biological pump globally occurs via the export of DOC. Effective export of DOM requires that the DOM produced by phytoplankton persist in surface waters until vertical exchange processes transport the material to depth. The mechanisms controlling the time scale for the accumulation and persistence of DOM in surface waters are dominated by biological processes that influence the amount and chemical character of the DOM produced and its consumption and decomposition by microbes. This project addresses these two coupled biological processes to examine controls on the accumulation of DOM during temperate diatom blooms. Diatom blooms are known to produce prodigious quantities of DOM upon entering nutrient stress with a chemical composition that varies with the type of nutrient limitation (Si or N). This variable composition likely influences the nutritional value of DOM to microbes driving species successions towards functional groups of heterotrophic prokaryotes that are best able to metabolize particular forms of DOM. To date each side of this coupled system of production/consumption has been examined independently. A few studies have examined how limitation by different limiting nutrients affects the chemical character of the DOM produced by phytoplankton, while others have focused on the fate of DOM without detailed understanding of the mechanisms influencing its initial chemical composition. This research project will examine both sides of this coupled process simultaneously to see how different forms of nutrient limitation drive the chemical character of DOM and the subsequent microbial response which together determine the fate of DOM produced during diatom blooms. The investigators will employ a combination of laboratory and field based approaches to: 1) Investigate how limitation by either N or Si impacts the chemical composition of the DOM released by diatom blooms. 2) Determine how differences in the composition of DOM produced by diatoms experiencing different nutrient stresses affects it susceptibility to heterotrophic microbial processing through changes in the productivity, growth efficiency and community structure of bacterioplankton. The research will focus on diatom blooms for two reasons. Diatom blooms are a regular feature in regions of the ocean where DOC export is known to be significant, i.e. such as the North Atlantic, making the fate of the DOM produced during blooms a potentially significant mechanism of C export. In addition, the direct release of DOM from phytoplankton is the best studied of numerous DOM production process providing the background for formulating hypotheses on how changes in DOM production and composition affect the bacterial response that drives its consumption. Preliminary data indicates that waters of the Santa Barbara Channel, California are an ideal model system for conducting this research because the spring diatom bloom is sufficiently predictable and amenable to the types of manipulations required for these studies, and ambient DOM concentrations are low for coastal waters allowing small changes in DOM concentrations to be resolved in both laboratory and field experiments.Broader Impacts: This research will contribute to the greater scientific goal of understanding the role of upper ocean food webs in carbon cycling. The findings will improve our basic understanding of DOM dynamics aiding modelers in the development of improved representations of key processes in ecosystem models. The project will enable the education of the next generation of biological oceanographers by training graduate students, and it will be leveraged to introduce oceanography into the curriculum of local K- 12 students to make them aware of the importance of the oceans to their lives and of the possibility of oceanography as a career choice.

智力优势：DOM在海洋系统表层沃茨中的停留时间是决定其对生物碳泵效率和大小贡献的主要因素。越来越多的证据表明，在某些海洋区域，表层海洋DOM的输出是在深海固存有机碳的高效途径。目前的估计是，20%的碳运输到深度的生物泵全球发生通过输出DOC。有效输出DOM要求浮游植物产生的DOM在表层沃茨中持续存在，直到垂直交换过程将物质输送到深层。控制表层沃茨中DOM积累和持续时间的机制主要是生物过程，生物过程影响DOM的产生量和化学性质，以及微生物对DOM的消耗和分解。本项目针对这两个耦合的生物过程，研究控制DOM的积累在温带硅藻水华。硅藻水华在进入营养胁迫时会产生大量的DOM，其化学组成随营养限制的类型（Si或N）而变化。这种可变的组合物可能会影响DOM的营养价值的微生物驱动物种演替的异养原核生物的功能群，最能代谢特定形式的DOM。到目前为止，这一生产/消费耦合系统的每一方都得到了独立的审查。一些研究已经研究了不同限制性营养盐的限制如何影响浮游植物产生的DOM的化学特征，而其他研究则集中在DOM的命运上，而没有详细了解影响其初始化学组成的机制。该研究项目将同时研究这一耦合过程的两个方面，以了解不同形式的营养限制如何驱动DOM的化学特性以及随后的微生物反应，这些反应共同决定了硅藻水华期间产生的DOM的命运。研究人员将采用实验室和现场相结合的方法：1）调查氮或硅的限制如何影响硅藻水华释放的DOM的化学组成。2)确定硅藻经历不同的营养胁迫产生的DOM组成的差异如何通过浮游细菌的生产力，生长效率和群落结构的变化影响其对异养微生物处理的敏感性。这项研究将集中在硅藻水华上有两个原因。硅藻水华是一个经常性的功能，在海洋地区的DOC出口是显着的，即如北大西洋，使在水华期间产生的DOM的命运一个潜在的重要机制C出口。此外，DOM从浮游植物的直接释放是众多DOM生产过程中最好的研究，为DOM生产和组成的变化如何影响细菌的反应，推动其消费的假设提供了背景。初步数据表明，加州州圣巴巴拉海峡的沃茨是进行这项研究的理想模型系统，因为春季硅藻水华是足够可预测的，并且适合这些研究所需的操作类型，并且沿海沃茨的环境DOM浓度较低，允许在实验室和现场实验中解决DOM浓度的微小变化。这项研究将有助于实现更大的科学目标，即了解上层海洋食物网在碳循环中的作用。这些发现将提高我们对DOM动态的基本理解，帮助建模者改进生态系统模型中关键过程的表示。该项目将通过培训研究生来教育下一代生物海洋学家，并将利用该项目将海洋学引入当地K- 12学生的课程，使他们认识到海洋对其生活的重要性以及海洋学作为职业选择的可能性。