Assimilation rates of dissolved organic carbon by photomixotrophic estuarine phytoplankton

光合营养河口浮游植物对溶解有机碳的同化率

• 批准号: 1260134
• 负责人: James Pinckney
• 金额: $ 35.57万
• 依托单位: University of South Carolina at Columbia
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-05-01 至 2017-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1260134&HistoricalAwards=false
• 关键词: Assimilation; rates; dissolved; organic; carbon

Phytoplankton, traditionally viewed as primary producers at the base of aquatic food webs, provide an energy source for higher trophic levels. However, some phytoplankton species function as both primary producers and heterotrophic secondary consumers. Phytoplankton that are photosynthetically competent but also take up and assimilate organic compounds are classified as facultative mixotrophs or, more simply, photomixotrophs. Unfortunately, we currently have few estimates of the proportion of the phytoplankton community that function as photomixotrophs, their rate of secondary production, or their temporal variation in abundance. Current paradigms about trophodynamics in marine systems do not consider this potentially important alternative pathway for energy flow for phytoplankton. The implication is that we may be missing a significant, fundamental process that affects carbon cycling and trophodynamics in estuarine systems. Furthermore, changes in the DOC composition due to anthropogenic alterations may result in changes in phytoplankton community structure and possibly promote the proliferation of harmful algal bloom species. In terms of ecosystem function, even moderate rates of photomixotrophy could potentially alter our current understanding of phytoplankton productivity, overall C turnover, competitive interactions, and energy transfer in estuarine environments. This project will use a novel approach to provide quantitative measures of the in situ rates and magnitudes of facultative heterotrophy in natural, estuarine phytoplankton communities over seasonal time scales in a representative estuarine ecosystem. The project will utilize a unique 14C radiolabeling technique to quantify the in situ assimilation rates of DOC by estuarine photomixotrophs and estimate the amount of DOC converted to phytoplankton biomass by photomixotrophy over seasonal time scales. This information will provide new insights into carbon dynamics in estuaries, the contribution of DOC to estuarine food webs, and the importance of photomixotrophy in determining the structural and functional characteristics of estuarine phytoplankton communities. INTELLECTUAL MERIT. The research will provide new insights into the potential importance of an alternative source of C (DOC) and pathway for phytoplankton production. Successful demonstration that a significant fraction of the production of estuarine phytoplankton is by photomixotrophy would have major implications for the way we currently view C flow in these systems. The project has a reasonable likelihood of altering the current paradigms for estuarine primary productivity as well as providing new evidence for mechanisms of competitive interactions between phytoplankton species in mixed, natural assemblages. The study will also provide first-order approximations of labile DOC turnover by phytoplankton and will be one of the few measurements ever obtained for an estuary. Research results will contribute to an improved knowledge of relevant and underlying ecophysiological, organismal, and community-level processes involving carbon cycling in an estuarine environment.BROADER IMPACTS. This project will address the broader impacts criterion of advancing discovery and understanding while promoting teaching, training, and learning. The project will provide support for a graduate student, summer support for an undergraduate assistant, and involve upper level undergraduates as lab interns. Undergraduate interns, recruited from the Marine Science Program at USC, will participate in sample analyses and learn to operate laboratory instrumentation. Furthermore, the field bioassays will be added as a module in a required Marine Science undergraduate field course, MSCI 460 - Field & Lab Investigations in MSCI.

浮游植物传统上被视为水生食物网底部的初级生产者，为更高的营养水平提供了能源。然而，一些浮游植物既是初级生产者，又是异养次级消费者。具有光合作用能力，但也吸收和同化有机化合物的浮游植物被归类为兼性混合营养生物，或更简单地说，光异养生物。不幸的是，我们目前几乎没有关于浮游植物群落中作为光养生物的比例、它们的次生生产率或它们丰度的时间变化的估计。目前关于海洋系统营养盐动力学的范例没有考虑到浮游植物能量流动的这一潜在的重要替代途径。这意味着我们可能遗漏了一个重要的、基本的影响河口系统碳循环和营养动力学的过程。此外，人为变化引起的DOC组成的变化可能会导致浮游植物群落结构的变化，并可能促进有害藻华物种的繁殖。在生态系统功能方面，即使是适度的光营养作用，也可能改变我们目前对浮游植物生产力、总碳周转、竞争性相互作用和河口环境中能量转移的理解。该项目将使用一种新的方法来提供对典型河口生态系统中天然河口浮游植物群落在季节性时间尺度上兼性异养的原位速率和程度的定量测量。该项目将利用独特的14C放射性标记技术来量化河口光养生物对DOC的原位同化速率，并估计在季节性时间尺度上光养生物将DOC转化为浮游植物生物量的量。这些信息将对河口的碳动态、DOC对河口食物网的贡献以及光营养在确定河口浮游植物群落的结构和功能特征方面的重要性提供新的见解。智力上的优点。这项研究将为浮游植物生产的替代碳源(DOC)和途径的潜在重要性提供新的见解。成功地证明，河口浮游植物生产的很大一部分是由光营养作用产生的，这将对我们目前看待这些系统中的碳流的方式产生重大影响。该项目有可能改变目前河口初级生产力的模式，并为混合自然组合中浮游植物物种之间的竞争性相互作用机制提供新的证据。这项研究还将提供浮游植物不稳定的DOC周转量的一级近似，这将是为数不多的针对河口的测量之一。研究成果将有助于更好地了解河口环境中涉及碳循环的相关和潜在的生态生理、生物和社区水平的过程。这个项目将解决更广泛的影响标准，即在促进教学、培训和学习的同时促进发现和理解。该项目将为一名研究生提供支持，为一名本科生助理提供暑期支持，并让高水平的本科生作为实验室实习生。南加州大学海洋科学项目的本科生实习生将参与样品分析，并学习操作实验室仪器。此外，野外生物化验将作为必修的海洋科学本科野外课程--MSCI 460--MSCI的野外与实验室调查--中的一个模块加入。