## 3 Results and Discussion
### Bacterial Community of ML Silage
#### 3.5.2 The Changes in the Dynamics of Relative Abundance among Bacterial Communities  
The changes in the dynamics of relative abundance among bacterial communities by phylum are shown in Figure 3. The relative abundance of _Proteobacteria_, _Firmicutes_ and _Bacteroides_ (up to 69%, 11% and 10%, respectively) indicated that they were the dominant phylum in pre-ensiled ML; similar results were observed by [PERSON] et al. [20]. With the prolonged ensiling time, the abundance of _Proteobacteria_ and _Bacteroides_ gradually decreased. After 30 days of ensiling, _Firmicutes_ became the most abundant phylum in ML silages treated with CA, and _Proteobacteria_ was still the most abundant phylum in the CK. Compared with the CK, the ML silages treated with CA showed a greater _Firmicutes_ abundance but lower _Proteobacteria_ abundance during all the stages of ensiling. _Proteobacteria_ decreased in the silages treated with CA, which might be because the CA could enhance the permeability of the outer membrane of Gram-negative bacteria and inhibit the growth of _Proteobacteria_[33]. The dynamics of relative abundance among bacterial communities by genus are shown in Figure 4. The relative abundance of bacterial communities was very low in the pre-ensiled ML. _Methylobacterium_ (4.01%) and _Sphingomonas_ (1.03%) were the dominant genera in pre-ensiled ML, which was consistent with the results for pre-ensiled alfalfa reported by [PERSON] et al. [34]. After 30 days of ensiling, _Lactobacillus_ (24.9%), _Kosakonia_ (9.6%), _Enterobacter_ (8.9%), _Methylobacterium_ (8.89%) and _Enterococcus_ (6.26%) were dominant in the CK, whereas _Lactobacillus_ was the only dominant genus in the silages treated with CA. _Lactobacillus_ is usually the dominant genus in silage due to its more active and rapid growth when the environmental pH declines. Some _Lactobacillus_ species are usually screened as inoculus due to their rapid growth, which enhances the fermentation quality, such as _Lactobacillus plantarum_ and _Lactobacillus casei_[17; 26]. The relative abundance of _Lactobacillus_ increased from 0.4 to 24.9, 60.7 and 47.3% in the CK and the silages treated with 1% CA and 2% CA after 30 days of ensiling, respectively. In the  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Items**} & \multirow{2}{*}{**Treatments**} & \multicolumn{4}{c}{**Ensiling Days**} \\ \cline{3-6}  & & **3** & **7** & **14** & **30** \\ \hline \multirow{4}{*}{Sobs} & CK & 1605 & 1339 & 1384 & 1373 \\  & CA1 & 1477 & 1402 & 1102 & 1305 \\  & CA2 & 1376 & 1499 & 1301 & 1337 \\  & CK & 2512  
same fermentation period, the silages treated with CA showed a higher _Lactobacillus_ abundance, which was consistent with the higher accumulation of lactic acid content (Figure 1). Moreover, _Lactobacillus_ abundance decreased in the silages treated with 1% CA after 14 days of ensiling, which might be due to the rapid depletion of fermentation substrates, which could not support the growth of _Lactobacillus_. The rapid depletion of fermentation substrate abundance might be responsible for the conversion of lactic acid to acetic acid in the silages treated with 1% CA because lactic acid becomes an alternative fermentation substrate for _Lactobacillus_. Similarly, [PERSON] et al. [15] observed that relatively high _Lactobacillus_ abundance corresponds to an elevation in acetic acid and a reduction in lactic acid. This conversion might be because different species of _Lactobacillus_ have different metabolic patterns and functions. Similar to _Lactobacillus_, _Enterococcus_ are desirable bacteria in the initial fermentation process, with the function of producing lactic acid to create a weak acid environment, which contributes to _Lactobacillus_ fermentation. In the silages treated with CA, the relative abundance of _Enterococcus_ decreased (Figure 5), which might be due to its low tolerance to the acidic environment caused by CA [17; 23].