Indigenous microbiota shapes divergent wine flavors across grape varieties within a single vineyard

The spontaneous fermentation of grape must, driven by indigenous microbial consortia, is a key process underpinning wine typicity and regional character. While large-scale biogeography shapes vineyard microbiomes, the relative influence of host grape variety versus annual vintage conditions on the fermenting ecosystem and its metabolic output remains poorly resolved under similar cultivation terroir conditions. To address this, a time-resolved study across six grape varieties from two consecutive vintages was analyzed fungal community dynamics via amplicon sequencing, and characterized volatile aroma profiles through HS-SPME-GC-MS during wine spontaneous fermentations. Our results demonstrate that grape variety is the principal determinant of the initial epiphytic microbiota and the ensuing successional trajectory. The differences observed between the 2023 and 2024 vintages secondarily modulated this dynamic, primarily through alterations in must chemistry, leading to distinct shifts in microbial network complexity and volatile compound accumulation. Crucially, the final aroma profile emerged from a multi-species interaction network, where a defined cohort of non-Saccharomyces yeasts acted as keystone taxa (mainly Hanseniaspora, Wickerhamomyces, Torulaspora, and Starmerella), contributing significantly to ester and higher alcohol production before the dominance of Saccharomyces. This work establishes a mechanistic framework linking varietal traits and vintage-related differences (2023 vs. 2024) to microbial community function and flavor formation, providing critical insights into the influence of variety and temporal variation on wine terroir expression.