Chronic drought differentially alters the belowground microbiome of drought susceptible and tolerant genotypes of Populus trichocarpa

Populus trichocarpa is an ecologically and economically important biofuel feedstock due to its fast growth rate. Belowground, P. trichocarpa interacts with diverse microorganisms. These plant-microbial interactions in the rhizosphere and root endosphere can bolster a variety of plant processes, ranging from pathogen suppression to drought tolerance, yet we know little about the impact of chronic drought stress on P. trichocarpa's belowground microbiomes. To investigate the interactive effect of chronic drought on belowground microbial communities across genetically different P. trichocarpa hosts, we assessed archaeal/bacterial and fungal communities within the root endosphere, rhizosphere, and surrounding bulk soil of selected genotypes in a long-term drought experiment in Boardman, OR, USA. We used 16S rRNA and ITS2 region amplicon sequencing across 16 distinct P. trichocarpa genotypes in plots with full or reduced irrigation. Eight of these genotypes have been previously identified as drought tolerant while the other eight genotypes were drought susceptible. Ultimately, associations of growth-promoting microbes in high-performing P. trichocarpa genotypes can be leveraged to improve biofeedstock productivity when exposed to drought conditions.