How do eukaryotic CO2 fixers co-exist with faster growing prokaryotic CO2 fixers in the oligotrophic ocean covering 40% of Earth?

该提案的主要目的是解释地球上最广泛的生物群的生态学基础--在开阔的少营养海洋中，真核二氧化碳固定物与生长更快的原核生物二氧化碳固定物共存。真核生物在地球上的大多数生物群落，例如陆地、淡水和一些海洋(沿海和极地水域)中主导着二氧化碳的固定，但有一个但也是主要的例外：覆盖地球40%的少营养海洋环流。为什么能量较高的真核生物尽管在环流中经历了数百万年的共同进化，仍然无法生长出比原核生物更强大的生物？我们假设，固定二氧化碳的真核生物和原核生物的共存是由周期性的营养脉冲进入地表阳光照耀的水域维持的，并补充了固定二氧化碳的真核生物对原核生物(即细菌)的摄食。利用我们的研究团队通过新的实验方法加强的综合专业知识，我们将解决以下问题：营养脉冲对固定二氧化碳的原核生物和真核生物的生长速度有什么影响？营养脉搏是如何影响细菌的？固定二氧化碳的真核生物选择性摄食是控制固定二氧化碳的原核生物生长的一种机制吗？我们将通过专注于大西洋和太平洋亚热带环流的实验工作来发现上述问题的普遍答案，这些环流占整个少营养开阔海洋面积的近四分之三。我们将调查的三个环流来自不同的地质时代，其枯竭的无机营养物质的组成也不同。我们将使用同位素示踪剂与流式细胞仪分类相结合，直接测量营养脉冲对微生物组特定生长率和细菌率的影响。流动分选微生物群的形态、分类特征和生理潜力将通过超微结构、分子和元基因组分析来表征。营养脉冲对二氧化碳固定原核生物和真核生物细胞生物量的影响将通过流动分选细胞的电子显微镜和能量色散X射线光谱来评估。实验证据将被综合成一个通用的概念，以解释在现代气候变化的影响下，由于贫营养化海洋的扩张，具有越来越重要的全球生物地球化学意义的最小的真核和原核生物二氧化碳固定物共存的机制。因此，该项目将在地球上最大的生物群中测试生物固定二氧化碳的无机营养控制程度。

The principal aim of the proposal is to explain the ecological basis of the most extensive biome on Earth - co-existence of eukaryotic CO2 fixers with faster growing prokaryotic CO2 fixers in the open oligotrophic ocean. Eukaryotes dominate CO2 fixation in most of Earth's biomes, e.g. terrestrial, freshwater and some marine (coastal and polar waters), with one but major exception: the oligotrophic oceanic gyres, covering 40% of Earth. Why have energetically superior eukaryotes been unable to outgrow prokaryotes despite millions of years of co-evolution in the gyres?We hypothesise that co-existence of CO2 fixing eukaryotes and prokaryotes is sustained by episodic nutrient pulses into the surface sunlit waters complemented by feeding of CO2-fixing eukaryotes on prokaryotes, i.e. bacterivory. Using the combined expertise of our research team strengthened by novel experimental approaches we will address the following questions: What is the impact of nutrient pulses on growth rates of CO2-fixing prokaryotes and eukaryotes? How do nutrient pulses affect bacterivory? Is selective feeding by CO2-fixing eukaryotes a mechanism for controlling growth of CO2-fixing prokaryotes?We will find out how general the answers to the above questions are by focusing on experimental work in the subtropical gyres of the Atlantic and Pacific Oceans, which comprise nearly three quarters of the total oligotrophic open ocean area. The three gyres we will investigate are of different geological ages and differ in composition of depleted inorganic nutrients. We will use isotopic tracers in combination with flow cytometric sorting to directly measure impact of nutrient pulses on microbial group-specific growth rates and bacterivory rates. Morphology, taxonomic identity and physiological potential of flow sorted microbial groups will be characterised by ultra-structural, molecular and metagenomic analyses. The effects of nutrient pulses on cellular biomass of CO2 fixing prokaryotes and eukaryotes will be assessed by electron microscopy of flow sorted cells coupled with energy dispersive X-ray spectroscopy. The experimental evidence will be synthesised into a generic concept to explain the mechanism of co-existence of the smallest eukaryotic and prokaryotic CO2 fixers of increasing global biogeochemical significance owing to expansion of the oligotrophic ocean under the influence of modern climate changes. Thus, the project will test the extent of inorganic nutrient control of biological CO2 fixation in the largest Earth's biome.