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.

智力优点：DOM在海洋系统表层水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，从表层海洋输出 DOM 是某些海洋区域深海封存有机碳的高效途径。目前估计，全球通过生物泵输送到深处的碳有 20% 通过 DOC 的输出发生。 DOM 的有效输出要求浮游植物产生的 DOM 持续存在于地表水中，直到垂直交换过程将物质输送到深处。控制地表水中 DOM 积累和持久性的时间尺度的机制主要由生物过程主导，这些生物过程影响 DOM 产生的数量和化学特性以及微生物对 DOM 的消耗和分解。该项目解决了这两个耦合的生物过程，以检查温带硅藻华期期间 DOM 积累的控制。已知硅藻华在进入营养胁迫时会产生大量的 DOM，其化学成分随营养限制类型（Si 或 N）而变化。这种可变的组成可能会影响 DOM 对微生物的营养价值，推动物种向异养原核生物功能群的演替，这些功能群最能代谢特定形式的 DOM。迄今为止，这个生产/消费耦合系统的每一方面都已被独立审查。一些研究探讨了不同限制性营养素的限制如何影响浮游植物产生的 DOM 的化学特性，而其他研究则关注 DOM 的命运，但没有详细了解影响其初始化学成分的机制。该研究项目将同时检查这一耦合过程的两侧，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，这些反应共同决定硅藻华期产生的 DOM 的命运。研究人员将采用实验室和现场相结合的方法来： 1) 研究 N 或 Si 的限制如何影响硅藻华释放的 DOM 的化学成分。 2) 确定经历不同营养胁迫的硅藻产生的 DOM 组成差异如何通过浮游细菌生产力、生长效率和群落结构的变化影响其对异养微生物加工的敏感性。该研究将重点关注硅藻华，原因有两个。硅藻华是已知 DOC 输出量较大的海洋区域（例如北大西洋）的常见特征，这使得硅藻华期间产生的 DOM 的命运成为 C 输出的潜在重要机制。此外，浮游植物直接释放 DOM 是众多 DOM 生产过程中研究最好的，为制定关于 DOM 生产和组成的变化如何影响驱动其消耗的细菌反应的假设提供了背景。初步数据表明，加利福尼亚州圣巴巴拉海峡的水域是进行这项研究的理想模型系统，因为春季硅藻华盛是可充分预测的，并且适合这些研究所需的操作类型，而且沿海水域的环境 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。 更广泛的影响：这项研究将有助于实现更大的科学目标，即了解硅藻的作用 碳循环中的上层海洋食物网。这些发现将提高我们对 DOM 动态的基本理解，帮助建模者开发生态系统模型中关键过程的改进表示。该项目将通过培训研究生来实现下一代生物海洋学家的教育，并将利用该项目将海洋学引入当地K-12学生的课程中，让他们意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。