## 3 Results
### Improvement of Soil Fertility by the Interaction of Biochar with Microbes  
After the Chinese cabbage was sowed in soil for 35 days, the rhizosphere soil was assayed for the soil's organic matter (Figure 4A). The content of the organic matter in the soil was increased with the increasing addition of biochar. When 5% biochar was added to the soil, the soil's organic matter content reached a maximum of 12.1 mg g\({}^{-1}\). On this  
Figure 3: Effect of biochar on relative abundances of microbial community at the genus levels.  
Figure 2: Effect of biochar addition in soil on microbial growth. Different letters on the top of bars indicated significant differences among the different treatments (\(p<0.05\)).  
basis, when microbes were applied together with biochar in the soil, the content of the soil's organic matter was further increased compared to that when only biochar was applied to the soil. When the microbes of _Ochroductrum_ sp. and _B. mucaliaginous_s were applied to the soil supplemented with 2% biochar, the the soil's organic matter was highest and was 36.7% higher than the control in the sterilised soil, as well as 7.0% higher than that in the soil with 2% biochar. Thus, the accumulation of organic matter in soil with both biochar and microbes was higher than that in soil with biochar alone. However, when 5% biochar and soil microbes were added to the soil, the content of the organic matter was significantly reduced, which was 16.3% lower than that in soil with 2% biochar and soil microbes.  
Figure 4: Improvement of soil fertility including the soil’s organic matter (**A**), available phosphorus (**B**) and available potassium (**C**) by the interaction of biochar with soil microbes in soil. Different letters on the top of bars indicated the significant differences among the different treatments (\(p<0.05\)).  
The available phosphorus/potassium contents were compared in different soil treatments. As shown in Figure 4B, there was no significant difference in the available phosphorus content regardless of whether biochar was applied to the soil or not, but the available phosphorus content in soil was increased significantly when the microbes of _Ochroductrum_ sp. and _B. mucilaginosus_ were applied to the soil. The maximal increment in the available phosphorus content was observed in the soil supplemented with 2% biochar and soil microbes, which was 45.5% higher than that in the sterilised soil without the addition of biochar and microbes. Its content in soil with both 2% biochar and microbes was 30% higher than that in soil with 2% biochar, and was 15.4% higher than that in soil with microbes. The interaction of biochar with microbes promoted the phosphorus-releasing activity of _Ochroductrum_ sp. ACCC10085 causing the increase in phosphorus content. However, when 5% biochar and soil microbes were added to the soil, the content of the available phosphorus in the soil was significantly reduced, which was 10.0% lower than that in soil with 2% biochar and soil microbes.  
To examine the influence of the interaction between biochar and microbes on the available potassium content in soil, both biochar and microbes were applied to the soil and the available potassium content was assayed (Figure 4C). Significant differences in the available potassium content were not detected in soil with varying amount of biochar, whereas the available potassium content was significantly increased when the microbes of _Ochroductrum_ sp. and _B. mucilaginosus_ were applied in the soil. The maximal increment in the available potassium content was observed in the soil supplemented with both 5% biochar and soil microbes, which was 46.4% higher than that in the soil without the addition of biochar and microbes. The content of soil-available potassium with both 5% biochar and microbes showed increases of 37.6% and 23.6%, respectively, compared to that in soil with 5% biochar alone and microbes alone.