## 3 Results and Discussion
### Bacterial Community of ML Silage
#### 3.5.2 The Changes in the Dynamics of Relative Abundance among Bacterial Communities
It is known that _Enterobacter_ is an undesirable facultative anaerobe in the fermentation process, being the principal competitor of the lactic acid bacteria for water-soluble carbohydrates under anaerobic conditions; its principal fermentation product is acetic acid [26]. [PERSON] et al. [35] reported that _Enterobacter_ was positively correlated with pH and negatively correlated with lactic acid. The high relative abundance of _Enterobacter_ could explain the relatively high pH (5.99) and acetic acid content (11.0 g/kg DM) in CK after 30 days of ensiling. Moreover, _Enterobacter_ can deaminate and decarboxylate amino acids, thereby enhancing ammonia-N production [36]. The relative abundance of _Enterobacter_ decreased from 8.96 to 0.83% with the addition of CA after 30 days of ensiling in this study (Figure 5), which might account for the lower acetic acid and ammonia-N content in the silages treated with CA. _Methylobacterium_ are facultative methylotrophic bacteria and are commonly symbiotic with plants. The relative abundance of  
Figure 4: Bacterial community and relative abundance by genus for mulberry leaf silages (M, pre-ensiled material; CK, the control; CA1, 1% citric acid; CA2, 2% citric acid; D3, 3 days of ensiling; D7, 7 days of ensiling; D14, 14 days of ensiling; D30, 30 days of ensiling). Figure 3: Bacterial community and relative abundance by phylum for mulberry leaf silages (M, pre-ensiled material; CK, the control; CA1, 1% citric acid; CA2, 2% citric acid; D3, 3 days of ensiling; D7, 7 days of ensiling; D14, 14 days of ensiling; D30, 30 days of ensiling). _Methylobacterium_ decreased from 9.78 to 1.12% and 8.89 to 2.00% in the silages treated with CA after 14 days and 30 days of ensiling, respectively, because it is strictly aerobic and neutroph (Figure 5) [37]. _Methylobacterium_ are considered to be undesirable bacteria in silage because it positively correlates with levels of ammonia-N and negatively correlates with lactic acid [38; 39]. The roles of _Splingomonas_, _Pantoea_ and _Kosakonia_ in silage are still unclear. [PERSON] et al. [40] observed that _Splingomonas_ is involved in nitrification under low dissolved oxygen conditions, which might resist the production of ammonia-N. The relative abundance of _Splingomonas_ decreased from 2.38 to 0.72% in the silages treated with CA after 30 days of ensiling. [PERSON] et al. [39] speculated that _Pantoea_ could preserve protein through their negative correlation with ammonia-N content. However, [PERSON] et al. [41] inferred that _Pantoea_ might compete for the fermentation substrate with lactic acid bacteria and cause an accumulation of butyric acid in silage because _Pantoea_ is separate from the _Enterobacter_ genus. Furthermore, [PERSON] et al. [42] reported that _Pantoea_ was more active in high-moisture environments and positively correlated with butyric acid. However, no butyric acid was detected in the current study, which might be due to the low relative abundance of _Pantoea_ (0.08%) in pre-ensiled ML. Similar to _Pantoea_, _Kosakonia_ was separated from the _Enterobacter_ genus. [PERSON] et al. [43] reported that _Kosakonia_ might reduce the ammonia-N content in silage due to its potential nitrogen fixing. The relative abundance of _Pantoea_ and _Kosakonia_ showed a similarly increasing trend in the CK during ensiling and was lower in the silages treated with CA in the current study. The relative abundance of _Pantoea_ and _Kosakonia_ decreased from 4.82 to 0.75% and 9.68 to 0.86% after 30 days of ensiling, respectively (Figure 5). The potential capacity of _Pantoea_, _Kosakonia_ and _Splingomonas_ to reduce ammonia-N might explain the relatively low ammonia-N in the CK after 30 days of ensiling (Table 2). However, the conventional functions of _Pantoea_ and _Kosakonia_ in silage are complicated; therefore, more research should be conducted to evaluate their function.