Collaborative Research: Orientation of elongate diatoms as a strategy for light harvesting

浮游植物与其所处的水动力环境有着密切的联系。以前的研究已经研究了湍流和剪切在营养吸收、斑块/层形成和捕食者-猎物相遇中所起的作用，但浮游植物定向在增加光捕获（以及最终的初级生产）方面的作用在很大程度上被忽视了。从新的原位全息成像中获得的令人信服的证据表明，链状形成硅藻的持续水平取向导致了一种假设，即在强分层区域，剪切流将导致细长的浮游植物形式系统地水平取向，从而最大化其在环境下行光场中的横截面积（和光捕获）。也有人认为，浮游植物大小和形状的变化是在某些水动力环境中赋予选择性竞争优势的基本特征，从而改变/调节群落组成。该项目的跨学科研究跨越了三个科学学科（生物学、光学和流体动力学），将促进我们对各种浮游植物的功能、它们与流体流动的相互作用以及由此对环境光学的影响的理解。该项目将支持一些本科生、研究生和博士后研究人员。该项目将先前收集的现场数据分析与实验室实验和建模相结合。为了进行现场数据分析，浮游植物的方向是通过未受干扰的水柱的原位全息图像进行量化的，同时还通过船载全息生物物理剖面仪收集了关键物理（湍流/剪切/分层）和光学参数的高分辨率测量。在实验室中，我们在定制的剪切槽中评估了不同种类和形态的浮游植物在受控层流和湍流条件下的定向响应，以确认长形浮游植物可以在特定的水动力环境中定向，从而最大限度地捕获光。此外，在不同剪切池处理下的受控生长/生理实验将探讨定向对生长、光合参数和生产力的影响。最后，项目结果将纳入对观测和模拟的物理、生物光学和生态相关参数的全球分析，以量化这一现象与初级生产和碳循环的相关性。

Phytoplankton have an intimate connection to the hydrodynamic environment in which they live.Previous studies have examined the role that turbulence and shear play in nutrient uptake, patch/layer formation, and predator-prey encounters, but the role of phytoplankton orientation to increase light capture (and ultimately primary production) has been largely overlooked. Compelling evidence of persistent horizontal orientation of chain-forming diatoms, obtained from novel in situ holographic imaging, has led to a hypothesis that in regions of strong stratification, shear flows will lead to systematic horizontal orientation of elongate phytoplankton forms that maximizes their cross-sectional area (and light capture) in the ambient downwelling light field. It has also been suggested that variations in phytoplankton size and shape are fundamental traits conferring selective competitive advantages in certain hydrodynamic environments, thus modifying/mediating community composition. The interdisciplinary research of this project crosses three scientific disciplines (biology, optics and fluid dynamics) and will advance our understanding of the function of diverse forms of phytoplankton, their interactions with fluid flows, and the resultant impacts on the optics of the environment. The project will support a number of undergraduate and graduate students, and post-doctoral researchers. This project combines analysis of previously collected field data with laboratory experiments and modeling. For the field data analysis, phytoplankton orientation is quantified from in situ holographic images of the undisturbed water column along with concurrent high resolution measurements of critical physical (turbulence/shear/stratification) and optical parameters collected from a ship-based holographic bio-physics profiler. In the laboratory, the orientation response of different phytoplankton species and morphologies is evaluated in custom built shear tanks under controlled laminar and turbulent conditions to confirm that elongate forms can orient in certain hydrodynamic environments to maximize light capture. In addition, controlled growth/physiology experiments in various shear tank treatments will explore the effects of orientation on growth, photosynthetic parameters and productivity. Lastly, the project results will be incorporated into a global analysis of observed and modeled physical, bio-optical and ecologically-relevant parameters, to quantify the relevance of this phenomenon to primary production and the carbon cycle.