Methods for the species-specific analysis of photosynthesis and top-down vs. bottom-up control in marine phytoplankton

浮游植物是所有水生食物网的基础。藻类群落中的物种在丰度、光合作用表现和产量上各不相同。这些差异可能会对食物链中的能量转移产生重要影响。产量低、数量多的物种可能不会被浮游动物捕食，因此不会对食物链中的能量转移做出贡献。相比之下，不太丰富的物种的高生产率可能表明它们优先被放牧。因此，与丰富的物种相比，它们对食物网络中的能量转移可能更重要。为了验证这些假设，位于荷兰耶尔塞克的荷兰皇家海洋研究所(NIOZ)将测试浮游植物物种特有的分析方法。流式细胞术可以快速表征浮游植物群落(细胞数量和荧光作为光合作用能力的衡量标准)，但只能粗略地区分藻类。结合显微镜和脉冲幅度调制(PAM)荧光法的单细胞分析要详细得多。可以准确地确定物种，同时可以测量它们的光合作用表现。这种方法很耗时，并且只允许测量有限数量的单元。流式细胞术和显微镜-PAM的结合似乎有望检验这些假说。在耶尔塞克NIOZ停留的三个月将用于优化所述的浮游植物单细胞分析方法。之后，将对北海浮游植物群落进行表征。在停留之后，所获得的知识将应用于一个计划中的研究项目，该项目将处理北海和波罗的海食物网络中的能量转移。

Phytoplankton builds the basis of all aquatic food webs. Species in an algal community differ in abundance and photosynthetic performance and production. These differences can have an essential effect on energy transfer in the food web. Abundant species with low production rates are possibly not grazed by zooplankton and thus do not contribute to energy transfer in the food web. In contrast, high production rates of less abundant species could indicate that they are grazed preferentially. Therefore, they might be of higher importance for energy transfer in the food web than abundant species.To test these hypotheses, methods for species-specific analysis of phytoplankton are to be tested in the Royal Netherlands Institute for Sea Research (NIOZ) in Yerseke, The Netherlands. Flowcytometry allows a fast characterization of the phytoplankton community (cell numbers and fluorescence as a measure of photosynthetic capacity), but only a coarse differentiation of algal groups. Single-cell analysis with a combination of microscope and pulse-amplitude modulation (PAM) fluorometry is much more detailed. Species can be determined accurately and their photosynthetic performance can be measured at the same time. This method is time-consuming and allows only for the measurement of a limited number of cells. A combination of flowcytometry and microscopy-PAM seems promising to test the hypotheses. The three months stay at the NIOZ in Yerseke will be used for optimizing the described methods for the single-cell analysis of phytoplankton. Afterwards, the phytoplankton community in the North Sea is to be characterized. Following the stay, the acquired knowledge will applied in a planned research project that will deal with energy transfer in the food web of the North and Baltic Sea.