Influence of drought severity on the blue grama (Bouteloua gracilis) rhizobiome

Plants rely on a diverse rhizobiome for resilience to environmental abiotic stress such as drought. With increasing severity and frequency of droughts worldwide due to climate change, untangling the relationships between plants and their rhizobiomes is vital to maintaining agricultural productivity and ecosystem diversity. However, untangling the complex network of plant-microbe interactions is complicated by diverse response above and belowground between different plant species and climate conditions. We conducted a greenhouse study using blue grama (Bouteloua gracilis), a drought-tolerant C4 grass native to shortgrass prairie across North American plains, to study the effect of increasing drought severity (control, mild drought, severe drought) on plant-microbe interactions. Previous results from this experiment have demonstrated physiological effects of increasing drought severity on blue grama which included an increase in belowground carbon allocation through root exudation and shifts in root exudate composition and specific root exudate metabolites concurrent with the gradient of drought severity. Here, we utilized 16S (bacteria + archaea, primers 515f/r808b) and LSU (fungi, primers LR22R/LR3) amplicon sequencing on the Illumina Miseq paired-end v3 600-cycle platform. Our results indicated that severe drought resulted in significant shifts in both the bacterial + archaeal and fungal rhizosphere communities. Specifically, using the change in relative abundance between ambient and drought conditions for each ZOTU as a surrogate for population-scale drought tolerance (e.g., as a response trait), we found that rhizosphere microbiome response to drought was non-randomly distributed across the phylogenies of both communities, suggesting that Planctomycetota, Thermoproteota (formerly Thaumarchaeota), and the Glomeromycota were the primary clades driving these changes. This study is an important contribution to furthering our understanding of the effects of drought on plant-microbe interactions and provides a platform for hypothesis generation for targeted functional studies of specific taxa involved in plant drought response.