Ecological and functional succession of the microbial community during pit mud maturation in Nongxiangxing Baijiu.

Pit mud (PM) microbiota play a vital role in Baijiu flavor formation, yet its ecological and functional succession during maturation remains incompletely elucidated. Here, physicochemical profiling, amplicon sequencing, and metagenomics were integrated to investigate 5-, 15-, and 30-year PM of Sichuan Tang Dynasty Laojiao cellars. Bacteria dominated the community (82.59%), followed by Archaea (16.99%), with Lactobacillus acetotolerans, Ruminococcaceae CPB6, and Methanobacterium paludis as major species. Discrepancies between sequencing methods were reflected in fungal taxa which had low-abundance. The 15-year PM exhibited distinct community and functional features, indicating a critical transitional stage. Functional analysis revealed that fermentation-relevant functions were mainly contributed by 7 key genera and 5 species. Physicochemical properties changed with pit age, characterized by increased moisture as well as decreased acidity and humic substance levels. Moisture, ammonium nitrogen (NH₄⁺-N), available phosphorus, and age were identified as key drivers shaping microbial composition and function. Moisture was identified as the most central mediator, establishing a three-tier cascade causal chain from microorganisms to nutrient accumulation. Functionally, 5-year PM sustained a simple, Lactobacillus-dominated, growth-oriented community; 15-year PM shifted toward aromatic compound degradation, nitrogen utilization, flavor-precursor synthesis; and 30-year PM developed into a stable, flavor-optimized ecosystem enriched in caproic-acid-producing Ruminococcaceae CPB6. Overall, PM maturation is driven by microbiome functional evolution, and the 15-year represented a pivotal period. This study provides a theoretical foundation for scientific PM management and targeted microbial regulation in Baijiu production.