## 3 Results and Discussion
### Microbial Composition Comparison  
The heatmap analysis was utilized to reveal the relative relationship of the top 40 microbial genera detected with the colors representing the species abundance (Figure 3A). It can be clearly observed from the heatmaps that in both evaluated samples, the abundance of _Lactobacillus_ and _Pediococcus_ in bacteria and _Kazachstania_ in eukaryotes was relatively stable during all six rounds of fermentation. Moreover, _Weissella_ was found to be relatively rich during the whole fermentation process, but its relative abundance decreased as the fermentation progressed. This decrease in _Weissella_'s abundance can be attributed to the increase in the types of species and the subsequent competition for nutrients, as was also observed in other studies [30; 31]. In addition, the abundance of _Geotrichum_ and _Kazachstania_ decreased gradually during the fermentation in the two fermented vegetables, whereas the abundance of _Enterococcus_, _Streptococcus_, _Clostridium_ and _Bacillus_ showed a trend toward a gradual increase in the fermentation process, with no change in their relative abundance in both fermentation systems even though they exhibited significantly opposite microorganisms. In fact, metagenomics sequencing allows the obtained data to be compared with a database to extract the information of microorganisms at the species level [32; 33]. Within the top 40 abundant species detected (Figure 3B), 30 species belonged to the genus of LAB. Within the LAB species, a varying behavior of abundance was observed along the fermentation process with species such as _L. paraplantarum_, _Levilactobacillus brevis_, _L. acettolerans_ decreasing in abundance during the fermentation in both samples. A UPGMA cluster analysis of the samples was performed based on the identified genus and species, demonstrating the higher similarity between the red radish samples. Figure 3: _Cont._  
To further understand the microbiota structure during paocai fermentation, NMDS and LDA Effect Size (LEfSe) was used to analyze the microbial differences. The NMDS analysis (Figure 1B) showed that the microbial community of the red radish and cabbage paocais displayed an obvious spatial structure during the fermentation process, where the composition of microorganisms in different vegetable fermentation systems exhibited greater differences (stress = 0.016 < 0.05). With the progress of the fermentation, the distance between spatial positioning of different fermented vegetable samples of the same round gradually increased, indicating that the influence of raw materials on the microbial composition increased with the increase of fermentation time. These observed results were consistent with the ANOSIM analysis, with the R value closer to 1 confirming the greater differences between groups with a \(p\)-value less than 0.05 indicative of the high reliability of  
Figure 3: (**A**) The heatmap analysis of the top 40 microorganisms at the genus level. (**B**) The heatmap analysis of the top 40 microorganisms at the species level. the test (Figure 1C,D). Towards the end of the third and fourth rounds of paocai fermentation, the different samples were significantly separated (R = 0.46, \(p\) = 0.009) with a further increase in distance at the end of the fifth and the sixth fermentation rounds (R = 0.89, \(p\) = 0.003). The aforementioned data further confirm that the microbial composition of different vegetable paocais presented continuous changes in the multiround fermentation with the differences significantly increasing along the fermentation time. LEfSe (Figure 1E) was used as an algorithm for high-dimensional biomarker discovery and identifying genomic features characterizing the differences between two or more biological conditions [34]. In this study, LEFSe was performed to evaluate the differences between the bacterial community structures of the different paocais. In the paocai, a total of 31 taxa were found to represent a remarkable difference in their relative abundance, with an LDA (log10) \(>\) 2.