Regulation of Primary Productivity in the Southern Ocean: Phytoplankton Photosynthesis Characteristics from Individual Cell Measurements

奥森：这个研究项目是美国联合全球海洋通量研究（JGOFS）南大洋项目的一部分，旨在：(1)更好地了解南大洋有机和无机碳通量，(2)确定调节这些通量的大小和变化的物理、生态和生物地球化学因素和过程，(3)将这些通量置于当代全球碳循环的背景下。美国在南大洋进行的全球海洋通量联合研究的核心任务是了解浮游生物食物网的组成，以及它将碳输送到深海的效率。提出的具体问题之一是该地区浮游植物生长和生产力的调节机制；光照限制、微量营养素可利用性和放牧压力都被用来解释经常观察到的高常量营养素浓度和相对较低生产力的持续存在。为了区分这些机制，本研究考察了在一系列环境条件下自然种群中浮游植物的光合特性。具体来说，它将通过单个细胞的叶绿素荧光诱导测量来估计不同浮游植物群的光化学效率和光系统2（PS2）的吸收横截面以及每个细胞的相对色素含量，这些可以通过显微镜或流式细胞术来区分。这些测量是对来自深度剖面和实验操纵的浮游植物组合的样本进行的，应该使我们能够区分浮游植物生长的限制因素。例如，微量营养素的限制应导致光化学效率低（反映功能PS2反应中心的损失），而低光限制（由于深度混合）将通过近表面细胞中的高荧光（即色素含量）表示。如果光合特性表明内在生长速率没有限制，则意味着放牧控制。所提议的测量的单个细胞性质将使我们能够评估给定水样中不同浮游植物群（或不同细胞）的状况，并明确地检查环境梯度或实验处理对给定物种的影响。此外，在测量过程中，浮游植物群落的组成将通过显微镜和流式细胞仪分析来表征。对自然组合和实验中细胞生理状态的观察，结合群落结构信息，将使我们能够评估光、铁和放牧作为南大洋生产力限制因素的相对重要性，并更好地解释浮游植物特性的大量测量结果，例如可以在高分辨率调查中获得FRR（快速重复率）荧光法。

95-30718 OLSON This research project is part of the US Joint Global Ocean Flux Study (JGOFS) Southern Ocean Program aimed at (1) a better understanding of the fluxes of carbon, both organic and inorganic, in the Southern Ocean, (2) identifying the physical, ecological and biogeochemical factors and processes which regulate the magnitude and variability of these fluxes, and (3) placing these fluxes into the context of the contemporary global carbon cycle. Central to the mission of the US Joint Global Ocean Flux Study in the Southern Ocean is an understanding of the composition of the planktonic food web, and the efficiency with which it transports carbon to the deep ocean. One of the specific questions being posed is the mechanism of regulation of phytoplankton growth and productivity in this area; light limitation, micronutrient availability and grazing pressure have all been proposed to explain the persistence of high macronutrient concentrations and the relatively low productivity often observed. To distinguish among these mechanisms, this research examines photosynthetic characteristics of phytoplankton in natural populations under a range of environmental conditions. specifically, it will estimate, from chlorophyll fluorescence induction measurements of individual cells, photochemical efficiency and absorption cross sections of photosystem 2(PS2) as well as relative pigment content per cell for different groups of phytoplankton, which can be distinguished either microscopically or flow cytometrically. These measurements, carried out on samples from depth profiles and experimentally-manipulated assemblages of phytoplankton, should allow us to distinguish among limiting factors for phytoplankton growth. For example, limitation by micronutrients should result in low photochemical efficiency (reflecting loss of functioning PS2 reaction centers), while low-light limitation (due to deep mixing) would be indicated by high fluorescence (i.e., pigment content) in near-surface cells. Grazing control would be implied if photosynthetic characteristics indicate no limitation of intrinsic growth rates The individual cell nature of the proposed measurements will allow us to evaluate the condition of different groups of phytoplankton (or different cells) in a given water sample, and to examine unambiguously the effects of environmental gradients or experimental treatments on given species. In addition, in the course of the measurements, the composition of the phytoplankton community will be characterized by microscopic and flow cytometric analysis. Observations of the physiological state of cells in natural assemblages and experiments, combined with information on community structure, will allow us to evaluate the relative importance of light, iron, and grazing as limiting factors for productivity in the Southern Ocean, and to better interpret bulk measurements of phytoplankton properties, such as can be obtained in a high resolution survey with FRR (fast repetition rate) fluorometry.