## 3 Results and Discussion  
### Richness and Diversity of Fungal Communities in Different Stages of Fermentation  
After sequencing the samples, rigorous quality control measures were implemented, including the removal of low-quality reads and chimera filtering, to obtain valid data. A total of 822,969 high-quality sequencing reads of fungal ITS DNA genes were generated from the samples (220-500 bp). On average, over 27,432 reads per sample were achieved. Furthermore, the rarefaction curves for all samples exhibited a distinct saturation plateau, with coverage exceeding 99%. This revealed that the vast majority of fungal phylotypes present in the Baijiu samples have been successfully identified. Chao1 and observed species (Sobs) values were calculated to determine species richness for Laobaign _Baijiu_ samples in different fermentation stages, and Shannon and Simpson indices were calculated to determine fungal diversity [19]. As shown in Table 1, combining Chao1 values with Sobs values of the whole fermentation process, the species richness of the fungal community was ranked as follows: E-6 > D-3 > D-1 > E-4 > E-5 > D-2. In regard to fungal diversity, the Shannon and Simpson indices of the fungal community were both ranked as follows: E-6 > D-1 > E-4 > D-3 > E-5 > D-2. The results showed that the richness and diversity of the fungal community in _Ercha_ stages were higher than those in _Dachu_. The highest and lowest values of alpha diversity, such as observed species, Chao1 richness, and Shannon indices, were both found in stages E-6 and D-2, respectively, which indicated that the fungal richness and diversity were highest at stage E-6 while lowest at stage D-2. This showed that the introduction of microorganisms in stages D-1 and E-4 disrupted the balance of the original fungal community; some of the initial fungal species died out, while those more adapted to the fermentation environment survived. The microbial population reached a new equilibrium in stage D-2. The addition of _Dapu_ in stage E-4 supplemented the fungal microorganisms so as to achieve the purpose of making full use of the substrate. Beta diversity was utilized to compare the compositions of microbial communities as well as assess differences between them. The fundamental result of this comparative analysis was a distance matrix, which delineated the community-level variations between two different samples. The community structures were analyzed using average linkage clustering [18]. At the genus level, the microbiota in stages D-1 and E-4 exhibited significant differences from those of stages D-2, D-3, E-5, and E-6, as evident from the hierarchical clustering tree constructed based on weighted UniFrac distances (Figure 1). In detail, the fungal community of stage D-1 differed significantly from that of stages D-2 and D-3, while the fungal community of stage D-2 was similar to that of stage D-3. In addition, the fungal community of stage E-6 had a significant difference from other samples. This indicated that the fungal community changed dramatically at stages D-1 and E-4 and that the microbial structure was gradually established after stages D-2 and E-5. \begin{table}
\begin{tabular}{c c c c c c c} \hline
**Sample** & **Clean Reads** & **OUT 1** & **[PERSON] 2** & **[PERSON] 2** & **[PERSON] 2** & **[PERSON] 2** & **Coverage 2** \\ \hline D-1 & 35,333 & 101 & 79.4 & 112.77 & 2.6767 & 0.764459 & 99.3 \\ D-2 & 35,795 & 63 & 41 & 56.791 & 0.8852 & 0.261388 & 99.7 \\ D-3 & 37,418 & 161 & 109.6 & 158.01 & 2.0635 & 0.531775 & 99.4 \\ E-4 & 36,706 & 98 & 78.8 & 100.02 &To further demonstrate the differences in species diversity between samples, a PCoA analysis of fungal structure during Laobaign _Baijiu_ fermentation was used to display the magnitude of differences between individual samples (Figure 2). The distance of different samples reflects the closeness of sample composition [20].