Group-Specific Diatom Silica Production in a Coastal Upwelling System

本研究将研究硅藻种类之间二氧化硅产量的分布，使用现有方法的新组合，以评估特定种类或属对硅藻二氧化硅总产量的贡献。通过利用沿海上升流系统和少营养亚热带环流中硅藻群落结构和硅藻生产的强烈对比，将检验关于硅藻种类之间硅藻生产分布的具体假设。一些证据支持这样一种观点，即负责大部分二氧化硅生产的硅藻从沿海系统中数量最丰富的物种转变为近海贫营养环境中相对罕见但非常大的细胞。这种转变改变了硅藻在区域食物网中的作用，并且由于决定浮游植物群在生物地球化学循环中的作用的许多过程是细胞大小的函数，因此这种转变对硅藻对上层海洋碳循环和生物泵的贡献的区域差异具有强烈的影响。本研究还试图了解硅限制在物种水平上调节硅藻二氧化硅生产中的作用。迄今为止，从南极的高硅水到沿海上升流系统和少营养亚热带环流，在每一个系统中都发现了硅的生产限制。对硅限制的实地研究很少伴随着对现有物种的检查。当研究确实有分类数据时，由于缺乏关于单个物种表现的信息，因此不可能在细胞之间分配所测量的速率，从而可能导致关于特定硅藻群对群落复合速率的贡献的错误结论。该项目将测试五个假设。每一个都与使用特定物种的数据来提高对调节硅藻在海洋食物网中的作用的因素的理解的总体主题有关。通过将使用放射性同位素32Si的硅产量的大量测量与使用荧光探针2-（4-吡啶基）-5（（4-（2-二甲氨基乙基-氨基氨基甲酸基）-甲氧基）苯基）oxazole或PDMPO的单个细胞硅沉积速率的定量测量相结合，将确定以下内容：物种特异性硅藻对群落总硅产量的贡献，硅藻种类之间硅产量分布的区域差异作为细胞大小的函数，物种特异性动力学参数控制物种竞争溶解硅的能力，以及特定硅藻群或物种的优势是否可以通过它们利用硅的能力和数量丰度来解释（而不是其他因素，如放牧或其他营养物质的限制）。更广泛的影响：来自野外组合的具体知识将提高对海洋中硅藻产生有机碳和二氧化硅的主要生物和生态驱动因素的理解。该数据集还将有助于确定沿海和少营养环流生态系统中食物网和生物地球化学模型中的关键物种，并测试实验室研究中硅藻营养吸收能力的知识是否代表实地混合群落中的硅藻。该项目还将为本科生在实验室和实地环境中提供研究经验，并将包括与UCSB海洋科学研究所的海洋到课堂（O2C）项目的科学外展人员合作设计的K-12外展项目，用于地区小学。目前，O2C每年为800个地区K-12教室的18,000多名学生提供服务，通过UCSB pi的海洋研究实例，将海洋科学带入学生的生活。

This study will examine the distribution of silica production among diatom species, using a novel combination of existing approaches, to evaluate the contributions of specific species or genera to total diatom silica production. Specific hypotheses regarding the distribution of silica production among species of diatoms will be tested by exploiting the strong contrasts in diatom community structure and silica production between a coastal upwelling system and in an oligotrophic subtropical gyre. Several lines of evidence support the idea that the diatoms responsible for the majority of silica production shifts from the most numerically abundant species in coastal systems to relatively rare, but very large, cells in offshore oligotrophic environments. This shift alters the role of diatoms in regional food webs and because many processes determining the role of phytoplankton groups in biogeochemical cycles are a function of cell size, such a shift has strong implications for regional differences in the contribution of diatoms to upper-ocean carbon cycling and the biological pump. This study also seeks to understand of the role of silicon limitation in regulating diatom silica production at the species level. Si limitation of silica production has been detected in every system examined to date, ranging from the high Si waters of the Antarctic, to coastal upwelling systems and the oligotrophic subtropical gyres. Field studies of Si limitation are rarely accompanied by examination of the species present. When studies do have taxonomic data the lack of information on the performance of individual species makes it impossible to allocate the measured rates among cells, potentially leading to erroneous conclusions about the contribution of specific diatom groups to community composite rates.The project will test five hypotheses. Each is related to the general theme of using species-specific data to improve understanding of the factors regulating diatoms' role in marine food webs. By combining bulk measures of silica production using the radioisotope 32Si with quantitative measures of silicon deposition rates by individual cells using the fluorescent probe 2-(4-pyridyl)-5((4-(2-dimethylaminoethyl-aminocarbamoyl)-methoxy)phenyl)oxazole, or PDMPO, the following will be determined: species-specific diatom contributions to total community silica production, regional differences in the distribution of silica production among diatom species as a function of cell size, species-specific kinetic parameters governing the ability of species to compete for dissolved silicon, and whether dominance of a particular diatom group or species can be explained by knowledge of their capacity to utilize Si and their numerical abundance (as opposed to other factors such as grazing or limitation by other nutrients).Broader impacts:Specific-specific knowledge from field assemblages will improve the understanding of the major biological and ecological drivers of organic carbon and silica production by diatoms in the sea. This dataset will also help identify key species for inclusion in food-web and biogeochemical models in coastal and oligotrophic gyre ecosystems, and test whether knowledge of diatom nutrient uptake capacity from laboratory studies are representative of diatoms in mixed communities in the field. This project will also provide research experiences for undergraduates in both the laboratory and field settings, and will include a K-12 outreach program designed in collaboration with scientific-outreach personnel from UCSB's Marine Science Institute's Oceans to Classroom (O2C) program for use in regional elementary schools. O2C currently reaches over 18,000 students in 800 regional K-12 classrooms annually bringing marine science to life for students using real-life examples of marine research by UCSB PIs.