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

9311113 Olson阿拉伯海JGOFS项目的一个核心任务是确定碳泵在该地区的运行效率，以及它如何响应物理强迫的变化。为了解决这些问题，我们需要分析食物网的结构，并确定它如何随着地理和时间梯度的变化而变化，在养分供应和水柱混合方面。阿拉伯海的生产性和低营养海洋系统并存，以及在相对恒定的太阳光照条件下，营养供应在非常高和非常低之间的规律振荡，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)利用双束流式细胞术和DNA特异性染色来区分异养和自养生物，对四个集约化站和选定的中间站的微浮游生物和纳米浮游生物的分布、丰度和光散射特性进行表征；(2)根据细胞数量的变化规律、单个细胞的光散射特性和深度剖面的DNA含量，估计特定浮游植物群的原位生长速度和对这些群的放牧压力；(3)通过测定经细胞分选纯化的浮游植物（特别是球石藻和微浮游）的C:N比值，验证了浮游植物在非季风期的生理N限制假说。不同浮游植物群对N富集的相对反应将通过碳酸盐14C孵育实验确定，然后进行细胞分选以获得细胞特异性生长速率。

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.