Collaborative Research: Investigating the relationship between size and the balance between carbon acquisition modes in mixotrophic protists

水生系统中的微型浮游生物传统上被分类为浮游植物或浮游动物。然而，越来越多的研究表明，很大一部分浮游生物属于第三类，混合营养体，它们可以利用光合作用和捕食来获得维持生长所需的资源。生物海洋学家对混合营养体的活动及其在水生食物网中的作用了解甚少，因为研究它们的方法存在挑战。在这个项目中，研究人员正在评估混合营养体的细胞大小与它们对光合作用和猎物摄取营养的依赖之间的关系。在浮游植物中，大小被认为是一种“主性状”，因为它影响代谢过程、生长速度、细胞组成和营养摄取动力学。虽然在一些数值模型中，大小已被用来约束混合营养活动，但细胞大小与营养获取模式平衡之间的功能关系尚未得到实证建立。作为更广泛影响的一部分，所有项目研究人员都参加了海洋碳和生物地球化学（OCB）混合营养工作组。项目团队包括早期职业研究人员，并通过已建立的本科生研究经验（REU）计划为博士后科学家、研究生和多名本科生提供培训。最后，教育拓展包括与科学教师专业发展计划的合作，为课堂和户外的海洋科学教学提供体验式科学课程和设备包。混合营养体同时通过光合作用和摄食获得碳，但每种营养模式对单个生物的贡献很少同时测量。对于每种营养模式的贡献如何在物种之间或随着生长限制因素的变化而变化，人们所知较少。研究人员正在对8种混合营养体进行孵化实验，以测量在一系列环境条件下从两种营养获取模式获得的碳比例。利用先进的同位素标记方法，研究人员正在评估混合营养体中细胞大小和营养策略之间的关系，有可能对海洋生态系统中的碳转移和转化有新的、广义的理解。混合营养体大小与其两种营养模式之间的关系可以改变生物海洋学家在细胞和群落水平上对混合营养体的认识，提高海洋生态系统模型的准确性，并能够更准确地预测浮游生物群落和生物地球化学循环如何随着海洋条件的变化而变化。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。

Microplankton in aquatic systems have traditionally been categorized as phytoplankton or zooplankton. However, a growing body of research has documented that a substantial portion of plankton belongs to a third group, mixotrophs, that can use both photosynthesis and prey ingestion to obtain resources necessary to maintain growth. Biological oceanographers have a poor understanding of mixotrophs’ activity and their role in the aquatic food web due to the methodological challenges of studying them. In this project, the investigators are assessing how mixotrophs’ cell size relates to their dependence on photosynthesis and prey ingestion for nutrient acquisition. Among phytoplankton, size is considered a “master trait” because it impacts metabolic processes, growth rates, cellular composition, and nutrient uptake kinetics. While size has been used to constrain mixotrophic activity in some numerical models, the functional relationship between cell size and the balance of nutrient acquisition modes has not yet been empirically established. As part of broader impacts, all project investigators are participating in an Ocean Carbon and Biogeochemistry (OCB) mixotrophy working group. The project team includes early career investigators and is providing training to a postdoctoral scientist, graduate student, and multiple undergraduates through an established research experience for undergraduates (REU) program. Finally, educational outreach includes collaboration with a professional development program for science teachers, providing experiential science curricula and equipment kits for teaching ocean science in the classroom and outdoors. Mixotrophs obtain carbon from photosynthesis and ingestion simultaneously but the contribution from each nutrient mode to an individual organism is rarely measured simultaneously. Less is known about how the contribution of each nutrient mode differs between species and or with changes in growth-limiting factors. The investigators are conducting incubation experiments with eight species of mixotrophs to measure the proportion of carbon obtained from both nutrient acquisition modes across a range of environmental conditions. Using cutting-edge isotopic labelling methods, the investigators are assessing the relationship between cell size and trophic strategy among mixotrophs, with the potential for new, generalized understanding of carbon transfer and transformation in marine ecosystems. A relationship between mixotroph size and their two nutrient modes could transform biological oceanographers’ understanding of mixotrophs at the cellular and community levels, improve the accuracy of ocean ecosystem models, and enable more accurate predictions of how plankton communities and biogeochemical cycling will be altered with changing ocean conditions.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.