EAGER: Metabolic mechanisms that align phytoplankton growth to the integrated growth environment

知识价值：虽然遥感提供了关于表层浮游植物叶绿素水平的定期全球视图，但与生态系统和生物地球化学研究更相关的属性是净初级生产力。实地碳同化测量通常用于发展叶绿素和NPP之间的关系，隐含的假设是，光和营养胁迫的影响得到充分理解，使同化等同于NPP。最近，PI对杜氏杜氏藻进行了研究，证明叶绿素特异性NPP和GPP在很宽的营养限制生长速率范围内是不变的，而短期碳同化速率变化很大（哈尔西等人，2010年a）。她的研究采用了一套广泛的测量方法，允许从PSII的初始光捕获反应到NPP的最终还原剂汇的光催化剂利用的会计。结果表明，虽然碳固定消耗了绝大多数的光合产物，只有一部分的总CO2固定（总碳初级生产，GPPC）最终纳入生物质（NPP）。剩余的，非常重要的，总二氧化碳固定的一部分在细胞周期的时间跨度内被氧化。这种暂时的细胞碳汇被称为“瞬时碳库”。利用瞬时碳库的代谢途径中的营养驱动变化直接影响基于14 C的光合作用测量，它们与NPP的关系，以及它们对参数化全球海洋生产叶绿素模型的适用性。本研究项目的总体目标是扩大D. tertiolecta的代表性物种的环境相关的群体，并解决如何占主导地位的代谢途径作用于瞬态碳库连接到细胞周期阶段，昼夜周期，和N-限制的增长。该研究项目将包括两项活动。首先，实验方法用于D。将使用另外五个物种重复三层膜。第二，关键的碳代谢途径，差异影响瞬时碳库取决于生长速度，将与细胞周期和昼夜周期的阶段。该PI将开发浮游植物光合作用的过程为基础的，生理的理解，它的关系，净增长，这些属性之间的代谢联系，以及它们对细胞周期和昼夜生长动态在不同的营养条件下的反应。这种理解是必不可少的破译所观察到的全球表层海洋叶绿素变化的生理组成部分，推进海洋初级生产的全球评估，并预测对气候变化的反应。更广泛的影响：本项目将为本科跨学科项目提供实践培训。PI将通过奖学金支持的计划，如霍华德休斯医学研究所奖学金计划和地下生物圈倡议，SBI，积极招募本科生，提供夏季实验室研究经验。在两年资助期结束时，他们将向生物海洋学计划提交一份更广泛的提案，其中包括对研究生培训的支持。此外，PI将根据对相关海洋科学主题的研究和理解，为教师开发演示和活动，强调海洋生理学。

Intellectual Merit:While remote sensing provides regular global views of surface phytoplankton chlorophyll levels (Chl), the more relevant property for ecosystem and biogeochemistry studies is net primary production (NPP). Field carbon assimilation measurements are commonly used to develop relationships between Chl and NPP, with the implicit assumption that the effects of light- and nutrient-stress are sufficiently well understood to allow assimilation to be equated with NPP. Recently, the PI conducted studies with Dunaliella tertiolecta demonstrating that Chl-specific NPP and GPP are invariant over a wide range of nutrient-limited growth rates, while short-term carbon assimilation rates vary dramatically (Halsey et al., 2010a). Her study employed a broad suite of measurement approaches that allowed an accounting of photosynthate utilization from the initial light harvesting reactions at PSII to the ultimate reductant sink of NPP. Results showed that, although carbon fixation consumes the vast majority of photosynthate, only a portion of the total CO2 fixed (gross carbon primary production, GPPC) is ultimately incorporated into biomass (NPP). The remaining, and very significant, portion of gross CO2 fixation was oxidized within the time span of a cell cycle. This temporary cellular carbon sink has been referred to as the 'transient carbon pool.' Nutrient-driven changes in metabolic pathways utilizing the transient carbon pool directly impact 14C-based measurements of photosynthesis, their relation to NPP, and their suitability for parameterizing global chlorophyll-based models of ocean production. The overarching objectives of this research project are to expand findings for D. tertiolecta to representative species of environmentally relevant groups, and to resolve how predominant metabolic pathways acting on the transient carbon pool are linked to cell cycle phase, diel cycle, and N-limited growth. This research project will consist of two activities. First, the experimental approach used for D. tertioleca will be repeated using five additional species. Second, key carbon metabolic pathways, that differentially influence the transient carbon pool depending on growth rate, will be linked to the cell cycle and phases of the diel cycle. The PIs will develop a process-based, physiological understanding of phytoplankton photosynthesis, its relationship to net growth, metabolic links between these attributes, and their responses to cell cycle and diel growth dynamics in varied nutrient conditions. This understanding is essential to decipher the physiological component of observed global changes in surface ocean Chl, advancing global assessments of ocean primary production, and predicting responses to climate variations.Broader Impacts:This project will give hands-on training for undergraduate interdisciplinary projects. The PIs will actively recruit undergraduate students through fellowship-supported programs such as the Howard Hughes Medical Institute fellowship program and the Subsurface Biosphere Initiative, SBI, to provide summer laboratory research experience. At the end of the two-year funding period, they will submit a more broadly encompassing proposal to the Biological Oceanography program that will include support for graduate student training. Furthermore, the PIs will develop presentations and activities for teachers that are based on research and understanding of related ocean science topics, emphasizing photophysiology.