Dynamic sinking behavior in diatoms: New insights from individual-based high resolution video observations

硅藻从光照充足的海洋上层下沉，负责将物质输送到深海，是控制海洋中这种草的总体丰度的一个重要因素。详细了解它们的下沉特征很重要，这样它们就可以在海洋动力学模型中准确地表示出来。人们一直认为，这些无鞭毛的微小细胞的所有成员都以大约相同的速率，以恒定的速率下沉，并且运动方向是向下的。然而，在单个细胞水平上对下沉速率的重新检查表明，这三个假设都是不正确的。利用复杂的光学和计算技术，这些研究人员正在研究单个硅藻细胞是如何下沉的，它们启动和停止的能力，并评估哪些部分实际上可以上升。这项研究将对硅藻如何通过改变它们的运动与外部环境相互作用产生新的见解。它还将解决这些种群中有多少实际上是向上移动的，从而加强营养物质向上移动到海洋光线充足的部分。这些是对小型单细胞物种如何与周围海洋相互作用的新见解，将极大地丰富我们对一个被认为已经很好理解的问题的理解。本课题将培养1名研究生和2名本科生。我们还提供了K-12活动，将全息仪器带入教室，以及我们研究所的公开讲座系列。硅藻下沉速率是重要的生活史特征，它控制着细胞表面的损失率和营养通量。正浮力（m / h速率）是最大硅藻细胞的一个属性，在垂直迁移生活史策略中起作用。然而，较小硅藻的速率通常由修正的Stokes方程来描述，并且通常假设是均匀且向下的。研究人员先前观察到，一个物种的下沉速率在一个样本内不是单调的，而是分布在一个平均值周围，可能是向上的，也可能是向下的，并且在第二个时间尺度上由细胞控制，从接近零到最大速度。因此，上升行为可以被限制在种群中具有显著下降率的一小部分。该项目的目标是确定这些特征有多普遍，确定这种独特的开始-停止下沉行为的作用，并通过一系列精心控制的实验室研究和广泛的硅藻物种来检查正浮力有多普遍。这些特征将在硅藻中出现的复杂形式/功能模式的框架内进行考虑。在停止/启动序列中，细胞周围的边界层差异很大，可以通过我们的技术直接可视化。在快速下沉过程中，营养物质向细胞的扩散加快；研究人员假设，通过使用恒定的体积下沉速率，细胞表面的扩散被低估了。这项工作只有在高分辨率相机和先进的处理技术的出现下才有可能实现，这些技术允许在动态水柱中量化颗粒和流体的流动。

The sinking of diatoms out of the well-lit upper layers of the ocean is responsible for transport of material to the deep-sea and is an important factor in controlling the overall abundance of this grass of the sea. Their sinking characteristics are important to understand in detail so they can be accurately represented in models of ocean dynamics. It has been assumed that all members of these non-flagellated, microscopic cells sink at approximately the same rate, at a constant rate, and that the direction of motion is downward. However, a re-examination of sinking rates at an individual cell level indicates that all three assumptions are incorrect. Using sophisticated optical and computing techniques, these researchers are examining how individual diatom cells sink, their ability to start and stop, and assessing what fraction can actually ascend. This study will yield new insights into how diatoms interact with their external environment by altering their movement through it. It will also address what fraction of these populations are actually moving upwards, thereby enhancing the movement of nutrients upward into the well-lit portions of the ocean. These are novel insights into how small unicellular species interact with the ocean around them and will significantly enrich our understanding of a problem that had been thought to be well understood. The project will train one graduate student and two undergraduate students in this research. Outreach is also provided by K-12 activities bringing holographic instruments into the classroom, and a public lecture series at our institute. Diatom sinking rates are important life history characteristics that control both loss rates and nutrient flux to the cell surface. Positive buoyancy (m per hour rates) is an attribute of the largest diatom cells and plays a role in a vertical migration life history strategy. However, rates in smaller diatoms are typically described from a modified Stokes equation and are generally assumed to uniform and downward. The investigators previously observed that a species sinking rate is not monotonic within a sample but is distributed around a mean value, may be both upward and downward, and is under cellular control from near-zero to maximum velocity over second time scales. Thus, ascending behavior can be limited to a small portion of a population with a substantial downward rate. The goal of this project is to determine how widespread these characteristics are, determine the role of this unique start-stop sinking behavior, and examine how pervasive positive buoyancy is using a series of carefully controlled laboratory studies and a broad suite of diatom species. These characteristics will be considered within a framework of the complex form/function patterns that occur in diatoms. Boundary layers around cells differ vastly during the stop/start sequence and can be directly visualized by our techniques. Nutrient diffusion to the cell is accelerated during fast sinking; the investigators hypothesize that diffusion to cellular surfaces has been underestimated by using a constant bulk sinking rate. This work is only possible with the advent of high resolution cameras and advanced processing that allows particle and fluid flow to be quantified in a dynamic water column.