Gemmell Brad J, Oh Genesok, Buskey Edward J, Villareal Tracy A
Deparment of Integrative Biology, University of South Florida, Tampa, FL 33620, USA Marine Science Department, University of Texas at Austin, Port Aransas, TX 78373, USA
Marine Science Department, University of Texas at Austin, Port Aransas, TX 78373, USA.
Proc Biol Sci. 2016 Oct 12;283(1840). doi: 10.1098/rspb.2016.1126.
Phytoplankton sinking is an important property that can determine community composition in the photic zone and material loss to the deep ocean. To date, studies of diatom suspension have relied on bulk measurements with assumptions that bulk rates adequately capture the essential characteristics of diatom sinking. However, recent work has illustrated that individual diatom sinking rates vary considerably from the mean bulk rate. In this study, we apply high-resolution optical techniques, individual-based observations of diatom sinking and a recently developed method of flow visualization around freely sinking cells. The results show that in both field samples and laboratory cultures, some large species of centric diatoms are capable of a novel behaviour, whereby cells undergo bursts of rapid sinking that alternate with near-zero sinking rates on the timescales of seconds. We also demonstrate that this behaviour is under direct metabolic control of the cell. We discuss these results in the context of implications for nutrient flux to the cell surface. While nutrient flux in large diatoms increases during fast sinking, current mass transport models cannot incorporate the unsteady sinking behaviour observed in this study. However, large diatoms appear capable of benefiting from the enhanced nutrient flux to their surface during rapid sinking even during brief intervening periods of near-zero sinking rates.
浮游植物沉降是一项重要特性，它能够决定光合层中的群落组成以及向深海的物质损失。迄今为止，对硅藻悬浮的研究一直依赖于总体测量，并假设总体速率能够充分捕捉硅藻沉降的基本特征。然而，最近的研究表明，单个硅藻的沉降速率与平均总体速率有很大差异。在本研究中，我们应用了高分辨率光学技术、基于个体的硅藻沉降观测以及一种最近开发的用于自由沉降细胞周围流动可视化的方法。结果表明，在野外样本和实验室培养物中，一些大型中心硅藻能够表现出一种新行为，即细胞会经历快速沉降的突发阶段，在数秒的时间尺度上与接近零的沉降速率交替出现。我们还证明了这种行为受细胞的直接代谢控制。我们在营养物质向细胞表面通量的影响背景下讨论了这些结果。虽然大型硅藻在快速沉降期间营养物质通量会增加，但目前的质量传输模型无法纳入本研究中观察到的不稳定沉降行为。然而，大型硅藻似乎能够从快速沉降期间其表面增强的营养物质通量中受益，即使在接近零沉降速率的短暂中间时期也是如此。
