Nutrient uplift in a cyclonic eddy increases diversity, primary productivity and iron demand of microbial communities relative to a western boundary current.
Nutrient uplift in a cyclonic eddy increases diversity, primary productivity and iron demand of microbial communities relative to a western boundary current.
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作者：
Doblin MA;Petrou K;Sinutok S;Seymour JR;Messer LF;Brown MV;Norman L;Everett JD;McInnes AS;Ralph PJ;Thompson PA;Hassler CS
全球海洋西边界流的增强将潜在地影响中尺度涡旋的产生，并重新分配微生物及其相关的生态和地球化学功能。为了了解涡流引起的微生物群落组成的变化以及它们如何控制生长，我们针对东澳大利亚洋流（EAC）地区，在气旋（冷芯）涡流（CCE）和邻近的EAC中采样微生物。光合和固氮微生物更多样化（2-10倍更大的香农指数）在CCE相对于EAC，和细胞大小分布在CCE占主导地位（67%）较大的微型浮游生物，而不是皮科和纳米尺寸的细胞在EAC。营养盐添加试验表明，氮是EAC中限制生长的主要营养盐，而铁是CCE中的次要限制营养盐。在重氮营养群落中，异养NifH基因序列在EAC中占主导地位，并归因于γ-，β-和δ-变形菌的成员，而CCE包含光合和异养重氮营养菌，包括束毛藻，UCYN-A和γ-变形菌。营养修正后的培养瓶的每日采样捕获了细胞，种群和群落水平的级联效应，表明微生物对营养供应的响应速度存在类群特异性差异。氮除了CCE社区增加picoeukaryotes叶绿素a的配额在24小时内，这表明营养隆起的漩涡造成的“绿化”的效果，以及浮游植物生物量的增加。经过三天的EAC和CCE，硅藻增加丰富的常量营养素（N，P，Si）和铁的修正案，而附着藻类和光养甲藻下降。我们的研究结果表明，气旋性涡旋增加氮输送到上层海洋，以潜在地减轻由于海洋变暖而增加分层的负面后果，但也增加了对铁的生物需求，这是维持大细胞光养生物生长所必需的，并可能在更长的时间尺度上支持固氮生物的多样性。
The intensification of western boundary currents in the global ocean will potentially influence meso-scale eddy generation, and redistribute microbes and their associated ecological and biogeochemical functions. To understand eddy-induced changes in microbial community composition as well as how they control growth, we targeted the East Australian Current (EAC) region to sample microbes in a cyclonic (cold-core) eddy (CCE) and the adjacent EAC. Phototrophic and diazotrophic microbes were more diverse (2–10 times greater Shannon index) in the CCE relative to the EAC, and the cell size distribution in the CCE was dominated (67%) by larger micro-plankton , as opposed to pico- and nano-sized cells in the EAC. Nutrient addition experiments determined that nitrogen was the principal nutrient limiting growth in the EAC, while iron was a secondary limiting nutrient in the CCE. Among the diazotrophic community, heterotrophic NifH gene sequences dominated in the EAC and were attributable to members of the gamma-, beta-, and delta-proteobacteria, while the CCE contained both phototrophic and heterotrophic diazotrophs, including Trichodesmium, UCYN-A and gamma-proteobacteria. Daily sampling of incubation bottles following nutrient amendment captured a cascade of effects at the cellular, population and community level, indicating taxon-specific differences in the speed of response of microbes to nutrient supply. Nitrogen addition to the CCE community increased picoeukaryote chlorophyll a quotas within 24 h, suggesting that nutrient uplift by eddies causes a ‘greening’ effect as well as an increase in phytoplankton biomass. After three days in both the EAC and CCE, diatoms increased in abundance with macronutrient (N, P, Si) and iron amendment, whereas haptophytes and phototrophic dinoflagellates declined. Our results indicate that cyclonic eddies increase delivery of nitrogen to the upper ocean to potentially mitigate the negative consequences of increased stratification due to ocean warming, but also increase the biological demand for iron that is necessary to sustain the growth of large-celled phototrophs and potentially support the diversity of diazotrophs over longer time-scales.