Comparative profiling of surface-sterilized leaf-associated microbiota and flavor-associated metabolites in two Gougunao tea cultivars across fresh and fermented leaf stages.

Black tea quality is governed mainly by endogenous enzymatic reactions during processing, whereas relationships between surface-sterilized leaf-associated microbiota and flavor-related chemical variation remain unclear. Here, differences between two Gougunao tea cultivars and between fresh- and fermented-leaf stages were investigated using 16S rRNA/ITS amplicon sequencing, untargeted LC-MS metabolomics, broadly targeted GC-MS volatile profiling in SIM mode, and sensory evaluation. The two cultivars were compared under the same standardized manufacturing procedure. Multivariate ordination and PERMANOVA showed significant differences in bacterial and fungal assemblages. Community composition differed significantly between G1 and G2 in both kingdoms, whereas a significant processing-stage effect was detected only for fungi. Bacterial communities were dominated by Sphingomonas and Methylobacterium, while fungal profiles were enriched in Dothideomycetes-affiliated genera, particularly Setophoma and Cladosporium. LC-MS and GC-MS analyses revealed differences in volatile and non-volatile features between the two tested cultivars that were evident in fresh leaves and remained detectable after processing. Although PICRUSt2 indicated broadly comparable predicted functional profiles among groups, cross-omics analysis after adjustment for cultivar and processing stage identified a limited set of adjusted genus-feature associations across both analytical platforms. Fungal genera from the same broad taxonomic class showed opposing directional association patterns, indicating taxon-specific rather than uniform class-level covariation. These findings describe microbial-chemical covariation in the two tested Gougunao tea cultivars and provide a basis for further investigation; they should not be generalized as a universal cultivar-dependent pattern, and direct microbial causality cannot be inferred.