## 3 Results
### Effect of BOF Addition on Soil Microbial Community Structure  
Based on the T-test, the relative abundance of nine fungal genera and nine bacteria genera displayed significant differences between PPB treatment and the control (Table 5). PBB addition greatly increased the richness of _Mucor_, _Rhizopus_, _Cunningham_, _Chitinophaga_, _Phenylobacterium_ and _Bacillus_. Nine genera were significantly decreased, including _Penicillium_, _Trichoderma_, _Fusarium_, _Serendipita_, _Artrilobotrys_, _Helvella_, _Splingomonas_, _Rhodanobacter_ and _Gemmatomonas_. In addition, the abundance of _Bacillus_ in the treatment with PBB addition was significantly higher than that in the control (Table 5), which was consistent with the expected results of fermentation with _B. subtilis_ Tipb55 inoculation.  
PCoA showed the relationship between the compositions of all soil microbial communities (Figure 2). As shown in Figure 2, the four repeats randomly collected from each treatment had similar positions and were located in different quadrants. Among them, the bacterial community (Figure 2a) had a contribution of 63.81% on the abscissa and 34.43% on the ordinate, and the fungal community (Figure 2b) had a contribution value of 70.62% on the abscissa and 13.23% on the ordinate. The ADONIS test (Table S1) showed that the bacterial (R\({}^{2}\) = 0.6162, \(p\) = 0.03) and fungal (R\({}^{2}\) = 0.6502, \(p\) = 0.031) communities of PBB and control were significantly different. In summary, the composition of the soil microbial community changed significantly with the PBB application.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Treatment**} & \multicolumn{3}{c}{**Fungal Community**} & \multicolumn{3}{c}{**Bacterial Community**} \\ \cline{2-7}  & **OTUs** & **Shannon** & **Chao1** & **ACE** & **OTUs** & **Shannon** & **Chao1** & **ACE** \\ \hline Control & 207 \(\pm\) 11 a & 2.78 \(\pm\) 0.09 a & 235 \(\pm\) 12 a & 237 \(\pm\) 11 a & 1474 \(\pm\) 119 a & 7.50 \(\pm\) 0.28 a & 1612 \(\pm\) 110 a & 1637 \(\pm\) 105 a \\ PBB & 138 \(\pm\) 6 b & 2.53 \(\pm\) 0.07 b & 160 \(\pm\) 15 b & 177 \(\pm\) 20 b & 1362 \(\pm\) 38 ab & 7.07 \(\pm\) 0.27 a & 1517 \(\pm\) 24 a & 1534 \(\pm\) 26 a \\ \hline \hline \end{tabular}  
* PBB, 4% bio-organic fertilizer addition; control, no PBB addition; Different letters within a column indicate significant differences among biochar-amended soils at \(p<0.05\).  
\end{table}
Table 4: Operational taxonomic unit (OTU) richness and diversity indices of PBB treatment.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Treatment**} & \multirow{2}{*}{**pH**} & **Electrical** & **Available P** & **Available K** & **Hydrolysable N** & **Organic** \\  & & **Conductivity (\%/cm)** & **(mg/kg)** & **(mg/kg)** & **(mg/kg)** & **Carbon (g/kg)** \\ \hline PBB4 & 6.79 \(\pm\) 0.02 a & 677.00 \(\pm\) 4.36 c & 72.76 \(\pm\) 1.41 b & 847.31 \(\pm\) 3.30 a & 357.39 \(\pm\) 5.66 a & 102.09 \(\pm\) 0.39 a \\ PBB2 & 6.56 \(\pm\) 0.00 b & 793.00 \(\pm\) 12.17 b & 80.86 \(\pm\) 1.29 a & 696.60 \(\pm\) 3.35 b & 301.52 \(\pm\) 38.82 b & 102.77 \(\pm\) 2.29 a \\ CK & 6.19 \(\pm\) 0.03 c & 1148.33 \(\pm\) 103.00 a & 72.75 \(\pm\) 0.16 b & 462.22 \(\pm\) 3.31 c & 288.63 \(\pm\) 10.90 b & 69.82 \(\pm\) 3.57 b \\ \hline \hline \end{tabular}  
* PBB4 represents 4% PBB addition; control, with no PBB addition. Different letters within a column indicate significant differences among biochar-amended soils at \(p<0.05\).  
\end{table}
Table 3: Effects of bio-organic fertilizer treatment on soil chemical properties.