The impact of abiotic and biotic stressors on belowground plant – microbe interactions in the biofeedstock Populus

Melissa A. Cregger, Nicholas C. Dove, Alyssa Carrell, Mindy Clark, Sara Jawdy, Dawn Klingeman, Wellington Muchero and Christopher W. Schadt, Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, Brandon Kristy, University of Tennessee, Knoxville, TN, Eric R. Johnston, Schneider National, Green Bay, WI, Allison Veach, Division of Biology, Kansas State University, Manhattan, KS

Background/Question/Methods
Over the past two decades, it has become increasingly clear that plant - microbe interactions alter the way in which plants grow and respond to abiotic and biotic stress. Unraveling these interactions between plant hosts and microbes could result in novel uses of microorganisms to aid in plant health and productivity and improve ecosystem functions such as carbon sequestration and nitrogen cycling. In this presentation, I will highlight how changing abiotic and biotic variables like water availability, soil nitrogen (N) status, and host susceptibility to fungal pathogens alters plant – microbe interactions across Populus species and genotypes within species. This presentation will highlight three studies that used amplicon sequencing, shotgun metagenomics, plant metabolomics, and measurements of plant physiology to explore how the plant and microbial community respond to these changing biotic and abiotic stressors.
Results/Conclusions
Overall, we found that shifts in soil N content, soil water availability, and pathogen abundance altered Populus rhizosphere and root endosphere community composition. Each factor differed in their explanatory value of variation in the microbiome. Interestingly, the effects of these changing stressors differed within genotypes and across species of Populus. Specifically: • Soil nitrogen content had pronounced effects on plant – microbe symbioses. Lower amounts of soil N resulted in an increase in the relative abundances of the N fixation gene nifH and an increase in symbiotic fungal taxa indicating the importance of plant-microbe symbiosis when nutrients are constrained.
• Reduced irrigation altered bacterial and fungal community composition across genotypes of trichocarpa. Interestingly, the diversity and relative of mycorrhizal fungi differed between drought resistant and drought susceptible P. trichocarpa genotypes.
• The abundance of two Populus pathogens, Sphaerulina musiva and Marssonina brunnea, differed amongst Populus genotypes in a common garden. However, the abundance of these two fungal pathogens explained only a modest amount of the variation (1-3%) in the larger microbiome.

These results highlight the complex nature of plant – microbe interactions and the potential for shifting roles in symbiotic organisms during environmental stress.