Genomic Science Program
U.S. Department of Energy | Office of Science | Biological and Environmental Research Program

Understanding the Effects of Populus—Mycorrhizal Associations on Plant Productivity and Resistance to Abiotic Stress

Authors:

María del Rosario Ramírez-Flores1* (ramirezflomd@ornl.gov), Alyssa A. Carrell1, Spencer Roth1, David Weston1, Dawn M. Klingeman1, Miranda Clark2, Sara Jawdy1, Dana L. Carper1, Gail Taylor3, Jamie McBrien1, Leah Burdick1, Ann Wymore1, David McLennan1, Tomás A. Rush1, Melissa A. Cregger1

Institutions:

1Biosciences Division, Oak Ridge National Laboratory; 2Safety and Operations Services Division, Oak Ridge National Laboratory; 3Plant Sciences, University of California–Davis

Goals

The overarching goal of this project is to create sustainable, managed ecosystems where important biofeedstocks can be produced while simultaneously maximizing soil health and mitigating adverse impacts of climatic change.

Abstract

Over the past 2 decades, it has become clear that symbiotic host–microbe interactions alter the way plants grow and respond to abiotic and biotic stress. Harnessing diversity within these plant–microbe associations provides an opportunity to create sustainable, multipurpose ecosystems. Within these managed ecosystems, science can produce energy necessary to meet global needs, while maximizing soil health and mitigating adverse impacts to climate. Therefore, to increase sustainability within DOE relevant biofeedstocks, researchers aim to develop plant-microbial pairings tailored for specific environmental conditions. First, researchers are identifying genetic variation within plant hosts to select for plants that are tolerant to abiotic stress. Next, scientists are complementing these plants with varied belowground microbial partners to alter plant performance and ecosystem carbon cycling.

First, this research group identified Populus genotypes that varied in their response to drought without associated microbial partners. Over the last 2 years, team members conducted a series of greenhouse experiments where they identified variation in Populus response to drought using both hyperspectral imaging and assessing changes in plant physiology across 39 genotypes of Populus trichocarpa, 39 of Populus deltoides, and 26 hybrid genotypes (P. trichocarpa x P. deltoides). Overall, researchers found differences in plant phenotype across genotypes and in response to drought. Interestingly, drought tolerant genotypes maintained higher levels of stomatal conductance during drought relative to drought susceptible genotypes. Genotypes in these experiments will be leveraged in manipulative studies with mycorrhizal isolates to examine if mycorrhizae can increase host stress tolerance in both drought susceptible and tolerant genotypes.

Next, this team characterized variation in mycorrhizal community dynamics across drought tolerant and susceptible P. trichocarpa genotypes planted in a common garden in Davis, CA. In February and July of 2022, researchers collected root and rhizosphere samples from drought tolerant and susceptible P. trichocarpa. Across these genotypes, the team found both arbuscular mycorrhizal (AM) and ectomycorrhizal (ECM) fungi colonized the roots, and drought tolerant genotypes had a greater percentage of hyphae, greater number of arbuscules, and a larger Hartig net compared to drought susceptible trees. Researchers found that mycorrhizal diversity and community composition varied between well-watered and drought treatments and across plant genotypes. Fungal isolations yielded potentially new ECM taxa that can be leveraged in future experiments.

Finally, in the fall of 2023, team members collected root and rhizosphere samples from P. trichocarpa and P. deltoides across natural precipitation gradients in Washington and Texas, respectively. Within these collections, researchers are characterizing variation in mycorrhizal community composition, colonization, and abundance. Culture collections are being developed for future experimentation.

Combined, these initial efforts highlight significant genetic variation in the response of Populus to drought and demonstrates variation in belowground mycorrhizal communities across drought tolerant and susceptible genotypes. Plant and fungal resources resulting from these experiments will be used to develop tailored plant-fungal partnerships to alter host abiotic stress tolerance and soil carbon cycling.

Funding Information

This work was supported by the U.S. DOE Office of Science through the BER program Early Career Research Program. The P. trichocarpa genome-wide association study (GWAS) plantation in Davis, CA, was developed and is maintained through the Center for Bioenergy Innovation, Bioenergy Research Center funded by BER.