Microbiomes of native and invading yellow starthistle

Invasive species may benefit from introduction to new regions where they can escape their natural enemies. Here we examined whether geographic patterns of microbial community composition support a role for enemy escape in the invasion of California, USA by yellow starthistle, a highly invasive plant in western North America. We used high-throughput sequencing of the 16S V4 region to characterize bacterial community composition in the phyllosphere, rhizosphere, leaves, and roots of plants from seven populations in California and eight populations in the native European range. We compared bacterial diversity between the native and invaded ranges, and with previously published estimates of plant genetic diversity within each population. Bacterial communities differed significantly among plant compartments, and between native and invaded ranges within compartments, with consistently lower diversity in the invaded range. Plant genetic diversity did not explain this pattern in bacterial diversity, but a positive relationship was found within ranges between bacterial diversity in roots and plant genetic diversity within populations. Our observation of lower bacterial diversity in the invaded relative to the native range of yellow starthistle is consistent with potential enemy escape, providing some of the first evidence for this scenario in plant microbiomes.