U.S. JGOFS: Microbial Communities in the Arabian Sea: Composition, Size, Spectra, and Growth Rates from Individual Cell Properties

9311113奥尔森在阿拉伯海的联合全球海洋观测系统项目的一个中心任务是确定碳泵在该地区的运作效率，以及它如何对物理强迫的变化作出反应。为了解决这些问题，我们需要分析食物网的结构，并确定它如何随营养物质供应和水柱混合的地理和时间梯度而变化。阿拉伯海多产和少营养海洋系统的并列，以及在相对恒定的太阳光照条件下营养物质供应的高、低速率之间的规律振荡，为我们提供了深入了解食物网调节过程的机会。在这个项目中，Olson博士将(1)使用双光束流式细胞仪和DNA特异性染色来区分异养和自养生物，以表征微浮游植物和纳米浮游生物在四个密集站点和选定中间站点的分布、丰度和光散射特性；(2)根据细胞数量、光散射特性和深度剖面中单个细胞的DNA含量的昼夜模式，估计特定浮游植物种群的原位生长速度和对这些种群的放牧压力；(3)通过细胞分选纯化浮游植物(特别是球藻和微浮游植物)的C/N比，检验浮游植物在非季风期生理上受N限制的假设。不同种类的浮游植物对氮素增加的相对反应将通过14C碳酸氢盐培养实验来确定，然后进行细胞分选，以获得细胞特定的生长率。

9311113 Olson A central mission of the JGOFS project in the Arabian Sea is to determine how efficiently the carbon pump operates in this region and how it responds to changes in physical forcing. To approach these problems we need to analyze the structure of the food web and determine how it varies with geographical and temporal gradients in nutrients supply and water column mixing. The juxtaposition of productive and oligotrophic oceanic systems in the Arabian Sea, and the regular oscillation between very high and low rates of nutrient supply under relatively constant conditions of solar illumination, offers opportunities for us to gain insights into food web regulation processes. In this project, Dr. Olson will (1) Characterize the distribution, abundance, and light scatter properties of the picoplankton and nanoplankton at the four intensive stations and at selected intermediate stations, using dual beam flow cytometry and DNA specific staining to distinguish heterotrophic as well as autotrophic organisms; (2) Estimate in situ growth rates of specific groups of phytoplankton, and grazing pressure on these groups, from diel patterns in cell number, light scatter properties and DNA content of individual cells from depth profiles; and (3) Test the hypothesis that the phytoplankton are physiologically N-limited during non-monsoon periods by measuring the C:N ratios of phytoplankton ( in particular, coccolithophores and picoplankton) purified by cell sorting. Relative responses of different groups of phytoplankton to N enrichment will be determined from 14C bicarbonate incubation experiments followed by cell sorting to obtain cell-specific growth rates.