Mixotrophic nanoflagellates can account for more than half of the bacterivory in the sunlit ocean, yet very little is known about their ecophysiology. Here, we characterize the grazing ecology of an open‐ocean mixotroph in the genus Florenciella (class Dictyochophyceae). Members of this class were indirectly implicated as major consumers of Prochlorococcus and Synechococcus in the oligotrophic North Pacific Subtropical Gyre, but their phagotrophic capabilities have never been investigated. Our studies showed that Florenciella readily consumed Prochlorococcus, Synechococcus, and heterotrophic bacteria, and that the ingested prey relieved nutrient limitations on growth. Florenciella grew faster (3 d⁻¹) in nitrogen‐deplete medium given sufficient live Synechococcus, than in nitrogen‐replete K medium (2 d⁻¹), but it did not grow in continuous darkness. Grazing rates were substantially higher under nutrient limitation and showed a hint of diel variability, with rates tending to be highest near the end of the light period. An apparent trade‐off between the maximum clearance rate (5 nL Florenciella⁻¹ h⁻¹) and the maximum ingestion rate (up to ∼ 10 prey cells Florenciella⁻¹ h⁻¹) across experiments suggests that grazing behavior may also vary in response to prey concentration. If the observed grazing rates are representative of other open‐ocean mixotrophs, their collective activity could account for a significant fraction of the daily cyanobacterial mortality. This study provides essential parameters for understanding the grazing ecology of a common marine mixotroph and the first characterization of mixotrophic nanoflagellate functional responses when feeding on unicellular cyanobacteria, the dominant marine primary producers in the oligotrophic ocean.

中文翻译：

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Florenciella（Dichtyochophyceae）的放牧生态生理学中的可塑性，它是一种混合营养型纳米鞭毛，它消耗原绿球菌和其他细菌

混合营养的纳米鞭毛虫可在阳光照射的海洋中占细菌总数的一半以上，但对其生态生理学知之甚少。在这里，我们描述了Florenciella属（Dictyochophyceae科）的一种开放海洋混养体的放牧生态。这个类的成员被间接牵连的主要消费者原绿球藻和聚球藻在贫营养的北太平洋副热带环流，但他们的phagotrophic能力从来没有被调查。我们的研究表明，Florenciella随便饮用原绿球藻，聚球藻和异养细菌，而且摄入的猎物缓解对经济增长的养分限制。给予足够的活合成乳球菌后，富氮培养基中的弗洛伦氏菌生长快（3 d ^-1），比富氮K培养基（2 d ^-1）中的弗洛伦氏菌生长快，但在连续黑暗中没有生长。在养分有限的情况下，放牧率显着较高，并显示出迪尔变异性的迹象，在光照结束时趋于最高。一个明显的折衷的最大清除率（5 NL之间Florenciella ^-1 ħ ^-1）和最大摄取速率（高达〜10猎物细胞Florenciella ^-1 ħ ^-1）的实验结果表明，放牧行为也可能会随着猎物的集中而变化。如果观察到的放牧率代表其他海洋混养动物，它们的集体活动可能占每日蓝藻死亡率的很大一部分。这项研究为理解普通海洋混合营养动物的放牧生态学以及以寡营养海洋中主要的海洋初级生产者为食的单细胞蓝细菌为食，对混合营养纳米鞭毛功能反应的第一个表征提供了必要的参数。