OCE-PRF Effects of below-ground complexity on seagrass sediment structure and function

该奖项全部或部分由《2021年美国救援计划法案》（公法117-2）资助。海洋沉积物通过代谢（“分解”）有机物或将其掩埋来控制海洋中碳的命运。然而，沉积物在某种程度上是一个“黑匣子”。在沉积物中，化学和生态学密切相关，因此很难确定哪些过程控制代谢。这个问题在海草床上更为明显，海草床是重要的沿海生态系统和高碳埋藏地。海草根部形成复杂的结构，与周围的沉积物交换营养和氧气，穴居动物可以通过混合和冲洗沉积物中的水来增加沉积物的代谢。这导致了海草沉积物代谢的可变性，目前还没有得到很好的解释。拟议的研究将把海草根结构和动物群落的差异与沉积物代谢率的变化联系起来。这项研究的结果将为管理和保护海草床的策略提供信息，并预测其宝贵的生态系统服务的变化。来自代表性不足群体的本科生将参与研究并指导他们自己的研究项目。该项目的研究结果将被改编成初中/高中的课程计划，以“隐藏的复杂性”为主题，向学生讲授自然界的物理结构、化学和生态之间的关系。本研究的总体目标是将海草根和根茎的复杂物理结构和地球化学活动整合到海草地下环境模型中，以评估该环境的哪些特征影响沉积物代谢。密集、复杂的根垫可以为沉积物提供更多的氧合，并推动更高的沉积物代谢率，根系的三维结构可以控制哪些动物可以生活在那里，进而控制动物的代谢增强活动。项目的具体目标是：(1)确定海草根和根茎形成的物理化学环境如何影响大型动物的功能多样性；(2)评估在不断扩大的海草床中不同位置的沉积物物理化学环境的变化如何对应沉积物代谢的变化；(3)评估海草类群之间的沉积物物理化学环境差异如何对应沉积物代谢的变化。物理结构将使用CT成像进行表征，地球化学模式将使用平面光电成像和靶向微剖面进行测量。利用多物理场建模技术，将构造和地球化学数据整合在一起，模拟海草根部周围沉积物的地球化学渗透。然后将这些模型结果与原位底栖生物室沉积物代谢的测量结果进行比较，以得出有关根对沉积物总氧合和动物行为的影响的结论。将无损CT和平面光电成像结合成一个统一的模型，将为海草沉积物的三维结构提供有价值的信息，而以前对海草沉积物的描述有限。开发的方法也将用于其他研究“不透明”系统（如沼泽、红树林和土壤）复杂性的研究人员。通过描述地下结构的变化，这项工作将提供对其过程的机制理解，然后将其与海草生态系统的更大规模模式联系起来，为海草的保护、恢复和管理提供有价值的知识，并为海草对气候变化的敏感性提供信息。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2).Marine sediments control the fate of carbon in the ocean by either metabolizing (“breaking down”) organic matter or burying it away. However, sediments are somewhat of a “black box”. Chemistry and ecology are closely connected in sediments, making it difficult to identify which processes control metabolism. This problem is even more pronounced in seagrass beds which are important coastal ecosystems and sites of very high carbon burial. Seagrass roots create complex structures that exchange nutrients and oxygen with the surrounding sediment, and burrowing animals can increase sediment metabolism by mixing and flushing water through sediments. This results in variability in seagrass sediment metabolism that is currently not well explained. The proposed research will link differences in seagrass root structure and animal communities to variation in sediment metabolism rates. The results of this research will inform strategies to manage and protect seagrass beds and anticipate changes in their valuable ecosystem services. Undergraduates from underrepresented groups will be involved in the research and mentored in their own research projects. The findings of the project will be adapted into a middle/high school level lesson plan on “Hidden Complexity” to teach students about the relationships between physical structure, chemistry and ecology in nature. The overarching goal of the proposed research is to integrate the complex physical structure and geochemical activity of seagrass roots and rhizomes into a model of the seagrass below-ground environment to assess which features of that environment affect sediment metabolism. Dense, complex root mats may oxygenate sediments more and drive higher sediment metabolism rates, and the 3D structure of the roots may control what fauna can live there and by extension the metabolism-enhancing activities the fauna perform. Specific goals of the project are to; (1) determine how the physical-chemical environment created by seagrass roots and rhizomes influences macrofaunal functional diversity, (2) assess how variation in the sediment physical-chemical environment at different locations in an expanding seagrass bed corresponds to variation in sediment metabolism, and (3) assess how differences in the sediment physical-chemical environment between seagrass taxa corresponds to variation in sediment metabolism. Physical structure will be characterized using CT imaging and geochemical patterns will be measured using planar optode imaging and targeted microprofiling. The structural and geochemical data will be integrated together using multiphysics modeling techniques to simulate geochemical permeance into the sediment around seagrass roots. These model results will then be compared to measurements of sediment metabolism from in situ benthic chambers to draw conclusions about the influence of roots on total sediment oxygenation and faunal behavior. The combination of non-destructive CT and planar optode imaging into a unified model will provide valuable information on the 3D structuring of seagrass sediments previously only described to a limited extent. The developed methodologies will also be of use to other researchers studying complexity in “opaque” systems, such as marshes, mangroves, and soils. By describing variation in below-ground structure, this work will provide a mechanistic understanding of its processes that can then be connected to larger-scale patterns in seagrass ecosystems, generating valuable knowledge for seagrass conservation, restoration, and management, and informing on seagrass susceptibility to climate change.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.