**3. Results**

#### *3.1. Results and Analysis*

3.1.1. Changes in Soil and Litter Chemical Characteristics

Different stand types had different effects on the chemical properties of the soil. In terms of soil pH and NH4+-N, moso bamboo and mixed 2 were significantly higher than Japanese cedar and mixed 1 (Table 1). In terms of soil NO3−-N, there were significant differences among Japanese cedar, mixed, and moso bamboo, and the trend of mixed 1 > moso bamboo > mixed 2 > Japanese cedar indicated that soil NO3−-N in the expansion area tended to increase during moso bamboo expansion. In terms of soil organic carbon and nitrogen, Japanese cedar and mixed 1 were significantly higher than moso bamboo and mixed 2, indicating that the contents of soil TOC and TN tended to decrease during the expansion of moso bamboo. In terms of litter organic carbon and the litter carbon–nitrogen ratio, Japanese cedar was significantly higher than moso bamboo. There was no significant difference in litter nitrogen (Table 1).

**Table 1.** Chemical properties (means ± se) of soil (Japanese cedar, mixed 1, mixed 2, and moso bamboo) and litter (Japanese cedar and moso bamboo). *p* values based on one-way ANOVA are shown. Means with the same letter indicate no significant difference in post hoc tests. Results with significant *p* values are shown in bold.


Notes: NH4+-N, ammonium nitrogen; NO3−-N, nitrate nitrogen; TOC, total organic carbon; TN, total nitrogen; TOC:TN: total carbon:nitrogen ratio. Capital letters next to means in the same column indicated significantly different within soil or litter.

#### 3.1.2. Changes in Fungal-Community Structure

The high-throughput sequencing results showed that there were significant differences in the number of soil fungi operational taxonomic units (OTUs) in the four vegetation types at the phylum, class, order, family, and genus levels (Table 2, Figure 1). At the phylum level, the numbers of OTUs in mixed 2 were significantly higher than in Japanese cedar. At the level of class and order, mixed 2 and moso bamboo were significantly higher than mixed 1 and Japanese cedar. At the family level, there were significant differences between Japanese cedar, mixed, and moso bamboo in the order of moso bamboo > mixed 2 > mixed 1 > Japanese cedar. At the genus level, mixed 1, mixed 2, and moso bamboo were significantly higher than Japanese cedar. This indicated that the number of OTUs in the soil fungal of moso bamboo exhibited an increasing trend.

**Table 2.** Effect of moso bamboo expansion on the number of OTUs of soil microbial fungi and bacteria in ANOVAs. Results with significant *p* values are shown in bold.


**Figure 1.** Effect of different vegetation types on the number of soil fungal and bacterial OTUs (means ± se): (**a**) number of soil fungal OTUs, (**b**) number of soil bacterial OTUs. Different letters above columns in the same color indicate significantly different.

The changes in the biodiversity of the soil fungal communities in the four vegetation types differed. There was no significant difference in the diversity index of the soil fungal community (goods coverage, Pielou's evenness, and simple), but there were significant differences in the Chao1, observed species, and Shannon indexes. Additionally, in terms of the Chao1 and observed species diversity indexes, mixed 2 and moso bamboo were significantly higher than Japanese cedar. In terms of the α-diversity Shannon index, moso bamboo was higher than Japanese cedar (Table 3, Figure 2).

**Table 3.** Effects of moso bamboo expansion on soil microbial fungi and bacteria α-diversity in ANOVAs. Results with significant *p* values are shown in bold.


**Figure 2.** Effect of different vegetation types on soil fungal and bacterial α-diversity index (means ± se). (**a**) Fungal a diversity Chao1 and observed species index, (**b**) fungal a diversity Shannon index, (**c**) bacterial a diversity Simpson index. Different letters above columns in the same color indicate significantly different.

The relative abundances of the soil fungal species at the phylum level of the four vegetation types differed. *Basidiomycota* and *Mucoromycota* were significantly higher in moso bamboo than in Japanese cedar and mixed 1. However, among *Ascomycota* species, Japanese cedar and mixed 1 were significantly higher than mixed 2 and moso bamboo (Figure 3).

#### 3.1.3. Changes in Bacterial Community Structure

The results of the high-throughput sequencing showed that there were significant differences in the number of soil bacterial OTUs in the four vegetation types at the order, family, and genus levels, but no significant differences at the phylum and class levels (Table 3, Figure 1). At the order level, Japanese cedar, mixed 1, and moso bamboo possessed significantly more OTUs than mixed 2. At the family level, moso bamboo and mixed 2 were significantly higher than Japanese cedar. At the genus level, Japanese cedar and mixed 1 were significantly higher than moso bamboo and mixed 2.

The diversity of soil bacteria in the four vegetation types differed. There was no significant difference in the soil bacterial-community diversity indexes (Chao1, goods coverage, observed species, Pielou's evenness, Shannon). There was a highly significant difference in the simple diversity index, in the order of Japanese cedar and mixed 1 > moso bamboo > mixed 2 (Table 2, Figure 2), indicating a downward trend in the soil bacterial diversity with moso bamboo expansion.

The relative abundances of the soil bacteria of the four vegetation types at the phylum level differed greatly. The three species of *Acidobacteria*, *Chloroflexi*, and *Gemmatimonadetes* were significantly higher in Japanese cedar and mixed 1 than in moso bamboo. Among the three species of *Proteobacteria*, *Verrucomicrobia*, and *Bacteroidetes*, the four vegetation types differed significantly in the order of mixed 2 > moso bamboo > Japanese cedar (Figure 3).

**Figure 3.** Effect of different vegetation types on species abundance of soil fungal and bacterial at the phylum level (means ± se). (**a**) Fungal species *Ascomycota* and *Asidiomycota*, (**b**) fungal species *Mucoromycota*,

(**c**) bacterial species *Proteobacteria* and *Acidobacteria*, (**d**) bacterial species *Actinobacteria* and *Chloroflexi*, (**e**) bacterial species *Verrucomicrobia* and *Gemmatimonadetes*, (**f**) bacterial species *Bacteroidetes*. Different letters above columns in the same color indicate significantly different.
