Geographic patterns and soil-to-bark microbial transmission shape microbiome assembly in tea trees

BACKGROUND: Understanding the ecological links in the microbiome of Camellia sinensis is vital for exploring beneficial interactions between microorganisms and economically important woody plants. RESULT: This study investigates the characteristics of microbial communities, source-sink dynamics, driving factors, and functional differentiation of tea tree bark and bulk soil in the primary tea-producing regions of Yunnan, China (City of Pu'er, Lincang, and Xishuangbanna). Using amplicon sequencing, FEAST source tracking, and functional prediction, we analyzed microbial community differences and ecological roles. Findings revealed that bulk soil may served as the microbial reservoir for bark, sharing all bark bacteria and 68.09% of bark fungi in Pu'er, with minimal reverse flow. Soil harbored higher alpha diversity dominated by Chloroflexi, Acidobacteriota, and Sordariomycetes, while bark selectively enriched Gammaproteobacteria, Cyanobacteriia, and Lecanoromycetes. Plant type mainly influenced bark bacterial communities (R²=76.49%, P < 0.001), whereas geographic location significantly impacted soil bacterial composition (R²=45.72%, P < 0.001) and fungi in both bark (R²=63.06%, P < 0.001) and soil (R²=78.84%, P < 0.01). Total nitrogen (TN) and organic matter (OM) in bulk soil emerged as the predominant factors influencing community variation both for niches of soil and bark. Functional differentiation was observed, with soil microbiomes primarily engaged in chemoheterotrophy and nutrient cycling, while bark microbiomes were more involved in carbon fixation and stress resistance. LEfSe analysis identified 30 bacterial and 64 fungal biomarkers (LDA ≥ 4, P < 0.05), including Xanthobacteraceae in soil and Pleosporaceae in bark. CONCLUSIONS: This study highlights soil's crucial role as a microbial reservoir and the impact of niche-specific factors, providing a framework to understand how microbial diversity is maintained and regulated along the Soil-Bark Continuum in tea plants.