Daily oscillations in photosynthetically active radiation strongly influence the timing of metabolic processes in picocyanobacteria, but it is less clear how the light−dark cycle affects the activities of their consumers. We investigated the relationship between marine picocyanobacteria and nanoplanktonic consumers throughout the diel cycle to determine whether heterotrophic and mixotrophic protists (algae with phagotrophic ability) display significant periodicity in grazing pressure. Carbon biomass of Prochlorococcus and Synechococcus was estimated continuously from abundances and cell size measurements made by flow cytometry. Picocyanobacterial dynamics were then compared to nanoplankton abundances and ingestion of fluorescently labeled bacteria measured every 4 h during a 4 d survey in the North Pacific Subtropical Gyre. Grazing of the labeled bacteria by heterotrophic nanoplankton was significantly greater at night than during the day. The grazing activity of mixotrophic nanoplankton showed no diel periodicity, suggesting that they may feed continuously, albeit at lower rates than heterotrophic nanoplankton, to alleviate nutrient limitation in this oligotrophic environment. Diel changes in Prochlorococcus biomass indicated that they could support substantial growth of nanoplankton if those grazers are the main source of picocyanobacterial mortality, and that grazers may contribute to temporally stable abundances of picocyanobacteria.

中文翻译：

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北太平洋亚热带环流异养和混合营养纳米浮游生物摄食活动的Diel振荡

光合活性辐射的每日振荡强烈影响微微蓝藻代谢过程的时间，但尚不清楚明暗循环如何影响其消费者的活动。我们研究了整个饮食周期中海洋微蓝藻和纳米浮游消费者之间的关系，以确定异养和混养原生生物（具有吞噬能力的藻类）是否在吃草压力下显示出显着的周期性。原绿球藻和聚球藻的碳生物量通过流式细胞术进行的丰度和细胞大小测量连续估计。然后，在北太平洋亚热带环流的 4 天调查期间，将微蓝藻动力学与纳米浮游生物丰度和荧光标记细菌的摄入量进行比较，每 4 小时测量一次。异养纳米浮游生物对标记细菌的放牧在夜间明显大于白天。混养纳米浮游生物的放牧活动没有显示出昼夜周期性，这表明它们可以连续进食，尽管速率低于异养纳米浮游生物，以缓解这种贫营养环境中的营养限制。原绿球藻生物量的 Diel 变化表明，如果这些食草动物是微微蓝藻死亡的主要来源，它们可以支持纳米浮游生物的大量生长，并且食草动物可能有助于暂时稳定的微微蓝藻数量。尽管其速率低于异养纳米浮游生物，但可以减轻这种贫营养环境中的营养限制。原绿球藻生物量的 Diel 变化表明，如果这些食草动物是微微蓝藻死亡的主要来源，它们可以支持纳米浮游生物的大量生长，并且食草动物可能有助于暂时稳定的微微蓝藻数量。尽管其速率低于异养纳米浮游生物，以减轻这种贫营养环境中的营养限制。原绿球藻生物量的 Diel 变化表明，如果这些食草动物是微微蓝藻死亡的主要来源，它们可以支持纳米浮游生物的大量生长，并且食草动物可能有助于暂时稳定的微微蓝藻丰度。