## 3 Results and Discussion
### The Impacts of Returning Biogas Slurry to the Field on the Yield of CO and Phosphorus Content
It correspondingly reduced the community abundance of _Actinomycteia_bacterium_, _Streptosporagiaceae_bacterium_, etc., indirectly affecting the relative abundance of major phosphorus metabolism genes such as _gcd_, _ppx-gppA_, _plnA_, _ptsS_, _ppk1_, and _spoT_ by altering the soil environment. It enhanced the solubility of inorganic phosphorus and the mineralization rate of organic phosphorus in the soil, and may weaken the competition between microorganisms and CO for phosphorus in the soil by inhibiting the transport of phosphorus between microbial cells, thus improving the utilization of soil phosphorus by CO.  
At the phylum level, as shown in Figure 3, the main phosphorus-solubilizing microbial phyla in the CO planting soil were _Actinobacteria_, _Proteobacteria_, _Chloroflexi_, and \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Treatments** & **Branch Phosphorus** & **Leaf Phosphorus** & **Fruit (with Seeds)** \\
**Content (mg kg\({}^{-1}\))** & **Content** & **Phosphorus Content** \\  & & **(mg kg\({}^{-1}\))** & **(mg kg\({}^{-1}\))** \\ \hline CK & 1161.760 \(\pm\) 144.17 & 704.625 \(\pm\) 24.38 & 707.201 \(\pm\) 27.55 \\ ZY1 & 1028.800 \(\pm\) 107.98 & 638.697 \(\pm\) 53.17 & 749.910 \(\pm\) 5.09 \\ ZY2 & 1431.043 \(\pm\) 101.33 & 669.567 \(\pm\) 65.59 & 699.330 \(\pm\) 15.64 \\ ZY3 & 915.413 \(\pm\) 42.77 & 673.953 \(\pm\) 15.77 & 711.750 \(\pm\) 18.43 \\ ZY4 & 1110.643 \(\pm\) 168.60 & 714.887 \(\pm\) 66.66 & 921.567 \(\pm\) 173.31 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Phosphorus content in different parts of CO from each treatment group. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Subunit** & \multicolumn{2}{c}{**Diversity Index**} & \multicolumn{2}{c}{**Richness Estimator**} & **Coverage** \\  & **[PERSON]** & **[PERSON]** & **[PERSON]** & **[PERSON]** & **Coverage** \\ \hline CK & 4.048 \(\pm\) 0.32 a & 0.063 \(\pm\) 0.02 c & 854.67 \(\pm\) 73.16 a & 854.67 \(\pm\) 73.16 a & 1 \\ ZY1 & 3.662 \(\pm\) 0.10 c & 0.097 \(\pm\) 0.01 a & 852 \(\pm\) 73.51 a & 852 \(\pm\) 73.51 a & 1 \\ ZY2 & 3.794 \(\pm\) 0.07 b & 0.081 \(\pm\) 0.01 b & 851.33 \(\pm\) 65.77 a & 851.33 \(\pm\) 65.77 a & 1 \\ ZY3 & 3.840 \(\pm\) 0.54 b & 0.085 \(\pm\) 0.02 b & 801.67 \(\pm\) 86.01 c & 801.67 \(\pm\) 86.01 b & 1 \\ ZY4 & 3.880 \(\pm\) 0.14 b & 0.069 \(\pm\) 0.01 c & 846 \(\pm\) 21.38 b & 846 \(\pm\) 21.38 a & 1 \\ CK & 4.048 \(\pm\) 0.32 a & 0.063 \(\pm\) 0.02 c & 854.67 \(\pm\) 73.16 a & 854.67 \(\pm\) 73.16 a & 1 \\ ZY1 & 3.662 \(\pm\) 0.10 c & 0.097 \(\pm\) 0.01 a & 852 \(\pm\) 73.51 a & 852 \(\pm\) 73.51 a & 1 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Microbial community diversity indices for each treatment group (a, b, c, indicate significant differences (\(p\) < 0.05) by Duncan’s test). _Acidobacteria_. After the return of biogas slurry to the field, the dominant phosphorus-solubilizing microorganisms in the soil were still the aforementioned four, accounting for approximately 80% of the total microbial biomass; however, compared to the CK, the application of biogas slurry somewhat increased the abundances of _Actinobacteria_, _Chloroflexi_, and _Acidobacteria_ in the soil, and somewhat decreased the abundance of _Proteobacteria_ (Figure 4). However, there was a significant impact on the abundances of non-dominant microbial phyla (Figure 4), with _Germatimonadetes_ (1.05-3.61%), _Candidatus_Rokubacteria_ (0.51-2.24%), _Candidatus_Eremiobacteraeota_ (0.30-1.21%), and Bacteroidetes showing significant decreases in abundance, whereas the abundances of unclassified-d-Bacteria and _Candidatus-Dormibacteraeota_ increased significantly (Figure 4). Figure 4: Inter-group variability test for microbial phylum-level communities (”_p_ < 0.05, \"\"_p_ < 0.01). The abundance of _Germatimonadetes_ decreased at low biogas slurry returns and increased at high biogas slurry returns. The abundance of _CandidatusRokubacteria_ was lower than that of the blank, and the abundance of _CandidatusEremiobacteraeota_ was higher than that of the blank in the biogas slurry treatment groups.