Plant species and soil type influence rhizosphere bacterial composition and seedling establishment on serpentine soils

Root-associated microbial communities influence plant phenotype, growth and local abundance, yet the factors that structure these microbial communities are still poorly understood. California landscapes contain serpentine soils, which are nutrient-poor and high in heavy metals, and distinct from neighboring soils. Here, we surveyed the rhizoplane of serpentine-indifferent plants species growing on serpentine and non-serpentine soils to determine the relative influence of plant identity and soil chemistry on rhizoplane microbial community structure using 16S rRNA metabarcoding. Additionally, we experimentally examined if locally adapted microorganisms enhance plant growth in serpentine soil. Plant species, soil chemistry, and the interaction between them were important in structuring rhizoplane bacterial communities in both the field and experimental soils. In the experiment, rhizoplane microbial community source influenced seedling survival, but plant growth phenotypes measured were largely invariant to microbial community with a few exceptions. Results from the field sampling suggest that plant species associate with specific microbial communities even across chemically distinct soils, and that microbial communities can differentially influence seedling survival on harsh serpentine soils.