Plant species within Streptanthoid Complex associate with distinct microbial communities that shift to be more similar under drought
Prolonged water stress can reduce plant growth and fitness and may shift rhizoplane microbial communities. Although drought affects microbial structure of many plant species, it is still poorly understood whether closely related plant species host distinct microbial communities or respond similarly to drought. To explore this question, eight members of the Streptanthus clade with varying affinity to serpentine were subjected to three watering regimes. Rhizoplane bacterial communities were described using 16S rRNA gene amplicon sequencing and we explored the impact of watering treatment and plant species on alpha diversity, differential abundance, and beta diversity of soil bacterial communities. Among most plant species, reduced watering also reduced alpha diversity, but plant species did not strongly impact alpha diversity. Drought treatment reduced microbial community dissimilarity among samples: bacterial communities were more similar when plants received less water. Watering altered the relative abundance of bacterial genera within Proteobacteria, Firmicutes, Bacteroidetes, Planctomycetes, and Acidobacteria, which responded similarly in the rhizoplane of most plant species. These results suggest that prolonged water stress in Streptanthus spp. can result in convergent microbial communities among plant species. We suggest the functional consequences of these shifts be examined to assess effects on plant and microbial fitness under drought conditions.