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系的生态基础-在开放的寡营养海洋中真核二氧化碳固定物与生长更快的原核二氧化碳固定物共存。在大多数地球生物群系中，真核生物主导着二氧化碳的固定，例如陆地、淡水和一些海洋（沿海和极地水域），但有一个主要例外：覆盖地球40%的少营养海洋环流。为什么能量上优越的真核生物无法超越原核生物，尽管在环流中共同进化了数百万年？我们假设，固定二氧化碳的真核生物和原核生物的共存是通过间歇性的营养脉冲进入阳光照射的水面，并辅以固定二氧化碳的真核生物对原核生物（即细菌）的摄食来维持的。利用我们研究团队的综合专业知识和新的实验方法，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？营养脉冲如何影响乳牙？固定二氧化碳的真核生物的选择性摄食是控制固定二氧化碳的原核生物生长的机制吗？我们将通过在大西洋和太平洋的副热带环流中进行的实验工作来发现上述问题的答案有多普遍，这两个环流占总少营养开放海洋面积的近四分之三。我们将研究的三个环流具有不同的地质时代，其无机营养物的组成也不同。我们将使用同位素示踪剂与流式细胞术分选相结合，直接测量营养脉冲对微生物群特异性生长速率和细菌率的影响。流动分类微生物群的形态、分类特性和生理潜力将通过超结构、分子和宏基因组分析进行表征。利用流式分选细胞的电子显微镜结合能量色散x射线能谱技术，研究营养脉冲对固定CO2的原核生物和真核生物细胞生物量的影响。实验证据将被综合成一个通用概念，以解释在现代气候变化的影响下，由于少营养化海洋的扩张，最小的真核和原核二氧化碳固定物共存的机制，其全球生物地球化学意义日益重要。因此，该项目将测试地球上最大的生物群落中无机养分对生物二氧化碳固定的控制程度。

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.