Poplar plants stabilize soil microbial communities during drought

Drought stress from climate change negatively impacts microbial activity, but the magnitude of stress responses is likely dependent on belowground interactions. We exposed Populus trichocarpa individuals and no plant bulk soils to extended drought (~0.03% GWC after 12d) and re-wet and a 12-d “recovery” period (continued irrigation) to determine the effects of plant presence in mediating soil microbiome stability to water-stress. Plant metabolomics indicated that drought exposure increased investment in C and N metabolic pathways (amino acids, fatty-acids, phenolic glycosides) regardless of recovery. Several metabolites (e.g., amino acids) positively correlated with root microbial alpha diversity, but not soil. Bacterial composition shifted with P. trichocarpa presence and with drought relative to irrigated controls whereas fungal composition only shifted with plant presence. The proportion of bacterial water-stress opportunistic OTUs (enriched counts in Drought) were high (~11%) at the end of drying, and maintained after re-wet, and recovery in bulk soils, but declined over time in soils with plants present. The proportion of sensitive bacterial OTUs (depleted) were similar among bulk soils and planted soils at drying, whereas during recovery the proportion of bulk soil sensitive OTUs increased and planted soils decreased. These data indicate that plants modulate soil and root associated microbial drought responses via tight plant-microbe linkages during extreme drought scenarios.