Microbial Nutrient Processes and Quality Determinants in Tea Plants (Camellia sinensis) Across Rhizosphere, Endosphere, and Phyllosphere

The plant-associated microbiome is increasingly recognized as a causal determinant of tea quality, yet its role in nutrient-to-quality conversion remains poorly synthesized. This review integrates evidence across three microbial domains—rhizosphere, endosphere, and phyllosphere—and examines how microorganisms mediate the transformation of soil nutrients into quality-contributing metabolites. The strongest causal evidence comes from the SynCom21 study, which demonstrated that a defined bacterial consortium directly enhances ammonium homeostasis and theanine biosynthesis in tea plants. Complementary mechanisms include a dual-layer biological nitrification inhibition strategy, whereby root-secreted theanine and litter-derived polyphenols jointly suppress soil nitrification. Beyond nitrogen, phosphate- and potassium-solubilizing microorganisms, arbuscular mycorrhizal fungi, and endophytic bacteria contribute to the mobilization of multiple nutrient elements. Tea ecosystems present distinctive challenges due to their acidic soils and exceptional accumulation of aluminum and fluorine, yet microbiome interactions with these elements remain largely unexplored. Cultivar–microbiome specificity, demonstrated at the genetic level through metagenome-wide association studies, necessitates cultivar-specific approaches for microbiome engineering. We map the current evidence hierarchy—from causal demonstration to correlation to speculation—and identify priority knowledge gaps including field validation of synthetic communities, long-term persistence of engineered microbiomes, and the aluminum– and fluorine–microbiome interface. Integrating multi-omics tools with synthetic community design offers a path toward microbiome-guided sustainable tea production.