Phyllosphere and rhizosphere microbiomes of an invasive shrub, Ardisia crenata, differ between its native and invaded ranges

Ecological underpinnings of the invasion success of exotic plants may be found in their interactions with microbes. Historically, two hypotheses, the Enemy Release Hypothesis (ERH) and the Enhanced Mutualism Hypothesis (EMH), have been proposed to explain microbial roles in plant invasions. Although recent high-throughput sequencing techniques have significantly expanded our understanding of plant-associated microbiomes and their functional guilds, few studies compare the microbiome associated with invasive plants between their native and exotic ranges. In this study, we extracted fungal and bacterial DNA within leaf endosphere, root endosphere and rhizosphere soil of an invasive plant, Ardisia crenata, sampled from their native range Japan and exotic range Florida, USA. By analyzing an Illumina sequencing dataset of them, we compared microbial community compositions and diversity between the native and exotic ranges. Furthermore, we tested whether the absence of pathogenic or mutualistic microbes in the native or exotic ranges can be detected in A. crenata as expected by the ERH or EMH. Our results revealed different community compositions across all plant parts between the native and exotic ranges for both fungi and bacteria. Two key findings stood out. Firstly, despite a higher microbial diversity in the rhizosphere soil in the exotic range than in the native range, the microbial diversity within leaf and root was notably lower in the exotic range compared to the native range. This implied the root endophytic microbes were not passively recruited from the locally available species pool in the soil. Secondly, the leaves in the native range harbored a greater number of plant pathogenic fungi than in the exotic range, supporting the ERH. These findings suggested potential importance of leaf pathogenic fungi in explaining the difference in population dynamics of invasive plants between their native and exotic ranges.