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

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 warmer waters, eutrophication, and disease. This project assesses how microbial symbionts protect eelgrass from chronic 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. Research activities are directly integrated into a cross campus course based undergraduate research experience that allows students at different campuses 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 changing baselines. 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.