Abstract: To gain a deeper understanding of the spatial coupling mechanism between microbes and flavor compounds at the “pit mud-jiupei” interface in the nongxiangxing baijiu fermentation system, this study systematically investigated the migration and colonization patterns of pit mud-sourced functional microbes and their roles in driving spatial heterogeneity in the metabolism of flavor compounds. High-throughput sequencing combined with multi-platform flavor compound analysis was employed for systematic spatial sampling of jiupei at different depths and horizontal distances, and core microecological functional modules were parsed using distance-decay models and weighted gene co-expression network analysis (WGCNA). The results indicated that the similarity of microbial communities between jiupei and pit mud decreased significantly with distance, with the upper layer showing a higher goodness of fit (R2 = 0.46) and the lower layer exhibiting faster decay, suggesting a clear spatial boundary for the influence of pit mud. Key flavor compounds such as ethyl caproate were significantly enriched at the 0 cm interface of the lower pit wall (maximum 433.09 µg/g), whereas ethyl lactate levels increased with distance from the pit wall (maximum 888.83 µg/g). The abundance of pit mud-sourced Caproiciproducens was high at the 0 cm interface (2.55%–26.52%) but dropped sharply away from the interface, while the pit core was dominated by Acetilactobacillus jinshanensis (relative abundance > 90%). WGCNA further identified a synergistic co-variation network centered on caproic acid-producing functional bacteria, caproic acid, and key esters (represented by ethyl caproate), which was primarily localized at the lower pit mud-jiupei interface. This study demonstrated that this interface is not merely a physical boundary but a critical metabolic ecotone determining the formation of typical flavor compounds, revealing a spatial functional decoupling mechanism between ethanol fermentation in the core and aroma formation in the periphery, thereby providing a scientific basis for the precise spatial regulation of baijiu quality.

Key words: nongxiangxing baijiu; spatial heterogeneity; pit mud; flavor compounds; microbial community