Collaborative Research: Applying the stress gradient hypothesis to understand the microbial facilitation of seagrass responses to thermal stress

大叶藻是一种海洋开花植物，生活在整个北半球的沿海地区。这些海洋植物为渔业提供了重要的栖息地，保护海岸线免受侵蚀，改善海洋酸化的负面影响，并有助于埋藏有机碳。然而，在过去的一个世纪里，由于各种环境压力，包括气候变暖、富营养化和疾病，大叶藻栖息地总体上出现了净损失。该项目评估微生物共生体如何保护大叶藻免受全球气候变化的压力。大鳗草与生活在其根部的各种微生物形成了密切的关系，但这些微生物的代谢和生理，以及它们在热胁迫下调节大鳗草健康中的作用，在很大程度上是未知的。该项目的结果有助于更好地确定这些微生物在不断增加的热应力下的作用，从而为旨在保护这些标志性生态系统的保护和恢复工作提供信息。因此，研究成果被分发给参与海草保护和恢复的利益相关者，包括加利福尼亚州海洋保护委员会、大法拉隆国家海洋保护区和全球海草苗圃网络，该网络旨在为海草种植恢复提供最佳实践。研究活动直接整合到基于跨校园课程的本科生研究体验中，这使得加州大学默塞德分校和加州大学戴维斯分校的学生在学年期间通过CURE（基于课程的本科生研究体验）相互参与研究设计。在一个快速变化的世界中，确定生物体和种群是否以及如何应对日益增加的压力是至关重要的。当前以压力梯度假说（SGH）为中心的理论预测，在压力升高的情况下，个体物种可能会更加依赖于促进或有益的相互作用，以缓冲恶劣的环境条件。尽管人们越来越认识到微生物组对几乎所有植物和动物宿主的健康和生存的重要性，但SGH及其推断结果很少用于评估环境胁迫下微生物组结构和功能的变化。该项目通过评估由全球气候变化（GCC）驱动的急性加热事件背景下海草-微生物组相互作用的变化，测试了SGH在海洋宿主-微生物组系统中的应用。该项目的具体目标是：(1)评估环境和实验升高温度条件下Zostera marina（大叶藻）微生物组的组装和功能，(2)通过量化可能影响微生物招募的小分子组成和释放到大叶藻根际，确定植物渗出物如何随温度升高而变化。(3)培养假定的有益菌群，实验测试在一定温度条件下，宿主微生物组的变化对宿主生长和存活的影响。该项目的结果扩展和修改了促进性相互作用如何随环境压力而变化的主流范式，包括显示微生物如何促进大叶藻的建立和生长的原始数据。在此过程中，该项目将有助于确定大叶藻微生物群在调节这种基础物种的健康、生存和维持方面的作用，这些物种分布在整个北半球的三个大洲。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。

Eelgrass is a marine flowering plant that lives within coastal regions throughout the Northern Hemisphere. These marine plants provide essential habitats for fisheries, protect coastlines from erosion, ameliorate negative impacts of ocean acidification, and help to bury organic carbon. Yet, in the past century there has been an overall net loss of eelgrass habitat due to various environmental stressors including climate warming, eutrophication, and disease. This project assesses how microbial symbionts protect eelgrass from global climate change stress. Eelgrass forms intimate relationships with a diverse set of microorganisms that live within their roots, but the metabolism and physiology of these microorganisms, and consequently their role in mediating eelgrass health under thermal stress, is largely unknown. Results from this project help better define the role of these microorganisms under increasing thermal stress and consequently inform conservation and restoration efforts that aim to protect these iconic ecosystems. As such, research is disseminated to stakeholders involved in seagrass conservation and restoration including the State of California Ocean Protection Council, the Greater Farallones National Marine Sanctuary and the Global Seagrass Nursery Network, which aims to bring best practices to seagrass cultivation for restoration. Research activities are directly integrated into a cross campus course based undergraduate research experience that allows students at UC Merced and UC Davis to engage with one another during the academic year on research design through a CURE (course-based undergraduate research experience). In a rapidly changing world, it is essential to determine if and how organisms and populations will cope with increasing stress. Current theory centered around the stress gradient hypothesis (SGH) predicts that under elevated stress individual species may become more reliant on facilitative or beneficial interactions that work to buffer harsh environmental conditions. Despite the growing recognition of the importance of the microbiome for the health and survival of almost all plant and animal hosts, the SGH and its corollaries have rarely been used in the evaluation of the changing structure and function of the microbiome under environmental stress. This project tests the application of SGH to a marine host-microbiome system by assessing shifts in the seagrass-microbiome interactions in the context of acute heating events as driven by global climate change (GCC). The specific goals of this project are to (1) assess the assembly and function of the Zostera marina (eelgrass) microbiome under ambient and experimentally elevated temperature conditions, (2) determine how plant exudation changes as a function of increased temperature by quantifying the composition and release of small molecules to the eelgrass rhizosphere that may influence microbial recruitment, and (3) culture putatively beneficial bacteria and experimentally test the effects of shifts in the host microbiome on host growth and survival under a range of temperature conditions. The results of this project extend and modify the prevailing paradigm of how facilitative interactions change with environmental stress by including primary data showing how microorganisms facilitate the establishment and growth of eelgrass. In doing so, this project will help define the role of the eelgrass microbiome in mediating the health, survival and maintenance of this foundation species found along three continents throughout the northern hemisphere.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.