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

硅藻的动态下沉行为：基于个体的高分辨率视频观察的新见解

• 批准号: 1537546
• 负责人: Tracy Villareal
• 金额: $ 51.06万
• 依托单位: University of Texas at Austin
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-09-01 至 2019-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1537546&HistoricalAwards=false
• 关键词: Dynamic; sinking; behavior; diatoms; New

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.

硅藻从光线充足的海洋上层下沉，负责将物质输送到深海，也是控制这种海草总体丰度的重要因素。详细了解它们的下沉特征​​非常重要，这样才能在海洋动力学模型中准确地表示它们。 假设这些无鞭毛的微观细胞的所有成员以大致相同的速率、恒定的速率下沉，并且运动方向是向下的。然而，对单个细胞水平的下沉率的重新检查表明，所有三个假设都是不正确的。 使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如何下沉、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其在外部环境中的运动来与其相互作用产生新的见解。 它还将解决这些种群中哪些部分实际上正在向上移动，从而增强营养物质向上移动到海洋光线充足的部分。 这些是关于小型单细胞物种如何与其周围海洋相互作用的新颖见解，并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。 该项目将培养一名研究生和两名本科生从事这项研究。 K-12 活动还提供了外展活动，将全息仪器带入课堂，以及我们研究所的公开讲座系列。 硅藻沉降率是重要的生命史特征，它控制着损失率和营养物质流向细胞表面的流量。正浮力（米每小时速率）是最大硅藻细胞的一个属性，在垂直迁移生活史策略中发挥着作用。然而，较小硅藻中的速率通常由修正的斯托克斯方程描述，并且通常假设为均匀且向下的。研究人员之前观察到，物种下沉速率在样本内不是单调的，而是分布在平均值附近，可能向上也可能向下，并且在第二时间尺度上受到细胞控制，从接近零到最大速度。因此，上升行为可能仅限于一小部分人口，而下降率却很大。该项目的目标是确定这些特征的普遍程度，确定这种独特的启停下沉行为的作用，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研究正浮力的普遍性。 这些特征将在硅藻中出现的复杂形式/功能模式的框架内考虑。在停止/启动序列期间，细胞周围的边界层差异很大，并且可以通过我们的技术直接可视化。快速下沉期间，营养物质向细胞的扩散加速；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。这项工作只有随着高分辨率相机和先进处理技术的出现才可能实现，这些先进处理技术可以量化动态水柱中的颗粒和流体流动。