An exploration of how plant and soil characteristics shape the Hypericum perforatum microbiome in three habitats

Saint John’s wort, Hypericum perforatum, is a medicinally and ecologically important perennial plant species that has a broad global distribution. Despite the species’ importance, little is known about the factors that structure its microbial communities and the identity of microbes that enhance plant growth and fitness. Here we aim to describe the microbial communities associated with Hypericum perforatum and elucidate factors that structure these communities. We collected H. perforatum root samples in three adjacent habitat types: wet and dry alvars (two types of limestone barren) and fallow agricultural fields (i.e. old-fields), in Jefferson County, New York. We used high-throughput amplicon sequencing to characterize the bacterial and fungal root microbiome. We also quantified aspects of the plant phenotype and soil characteristics to evaluate habitat variables that correlate with the root microbiome. Habitat and plant height were correlated with shifts in microbial community composition. We identified two bacterial taxa positively associated with plant height, both belonging to the bacterial phylum Actinobacteria. This work contributes to our understanding of the environmental determinants of microbial community composition and identifies microbial taxa that may be important in promoting plant growth.