# Sloping Farmlands Conversion to Mixed Forest Improves Soil Carbon Pool on the Loess Plateau
## 3 Results
### Soil Microbial Activities in Different Vegetation Restoration Types  
All vegetation restoration had a significant effect on soil enzyme activities (Table 2). Following farmland abandonment, grassland exhibited decreased urease activities (\(p<0.05\)), and shrubs, forests and the mixed forests exhibited increased urease activities (\(p<0.05\)) (Table 2). Overall, amylase and polyphenol oxidase activities were reduced by vegetation restoration, but phosphatase, saccharase, cellulase, and catalase activities increased compared to sloping farmland (\(p<0.05\)) (Table 2).  
All studied vegetation restoration types significantly increased MBC, MBN, and MBP contents compared with sloping farmland (\(p<0.05\)) (Figure 4), suggesting that microbial biomass was increased due to vegetation restoration, which resulted in higher BR in grasslands, shrubs, forests and mixed forests (Figure 4). Among the types studied, the  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline
**Land** & **Sacharase** & **Cellulose** & **Urease** & **Amylase** & **Phosphatase** & **PolyphenylO oxidase** & **Catalase** \\
**Use** & **(mg Glucose** & **(mg Glucose** & **(mg NH\({}_{4}\)**********\(\cdot\)**N** & **(mg Maltcose** & **(mg Phenol** & **(mL 0.01 N** & **(mL 0.01 N** \\
**Types** & **g\({}^{-1}\) h\({}^{-1}\))** & **g\({}^{-1}\) h\({}^{-1}\))** & **g\({}^{-1}\) h\({}^{-1}\))** & **g\({}^{-1}\) h\({}^{-1}\))** & **g\({}^{-1}\) h\({}^{-1}\))** & **I\({}_{2}\) g\({}^{-1}\))** & **KMnO\({}_{4}\) g\({}^{-1}\))** \\ \hline SF & 1.05 \(\pm\) 0.09 c & 1.44 \(\pm\) 0.19 b & 0.57 \(\pm\) 0.14 d & 1.23 \(\pm\) 0.12 ab & 0.32 \(\pm\) 0.13 c & 2.81 \(\pm\) 0.19 a & 0.49 \(\pm\) 0.17 d \\ GL & 2.49 \(\pm\) 0.18 b & 2.13 \(\pm\) 0.19 a & 0.40 \(\pm\) 0.12 e & 1.01 \(\pm\) 0.12 bc & 1.29 \(\pm\) 0.22 b & 2.16 \(\pm\) 0.19 b & 0.64 \(\pm\) 0.18 c \\ SL & 2.17 \(\pm\) 0.27 b & 1.95 \(\pm\) 0.19 a & 1.77 \(\pm\) 0.21 a & 0.90 \(\pm\) 0.23 c & 1.32 \(\pm\) 0.27 b & 2.11 \(\pm\) 0.23 b & 0.69 \(\pm\) 0.09 c \\ FL & 3.27 \(\pm\) 0.34 a & 1.97 \(\pm\) 0.18 a & 1.27 \(\pm\) 0.11 b & 0.85 \(\pm\) 0.22 c & 1.18 \(\pm\) 0.21 b & 1.21 \(\pm\) 0.20 b & 0.96 \(\pm\) 0.21 a \\ ML & 2.54 \(\pm\) 0.24 b & 1.95 \(\pm\) 0.26 a & 0.60 \(\pm\) 0.17 d & 1.05 \(\pm\) 0.18 bc & 1.56 \(\pm\) 0.27 a & 1.98 \(\pm\) 0.27 b & 0.80 \(\pm\) 0.19 ab \\ \hline \end{tabular}
\end{table}
Table 2: Soil enzymes activities in different vegetation restoration types. Note: SF, Sloping farmland; GL, Grassland; SL, shrubland of _Caragana korshinskii_; FL, forestlands of _Robinia pseudoacacia_; ML, mixed forests of _Robinia pseudoacacia_ + _Caragana korshinski_. Different lower-case letters mean significant differences in different land use types at 0.01 level (\(p<0.01\)). Data are Means \(\pm\) SE. \(n=3\).  
Figure 3: Soil N and P nutrients in different vegetation restoration types. TN (**a**), total nitrogen; AN (**b**), available nitrogen; TP (**c**), total phosphorus; AP (**d**), available phosphorus. Note: SF, Sloping farmland; GL, Grassland; SL, shrubland of _Caragana korshinskii_; FL, forestlands of _Robinia pseudoacacia_; ML, mixed forests of _Robinia pseudoacacia_ + _Caragana korshinski_. Different lower-case letters above the error bars indicate significant differences in different land use types at 0.05 level (\(p<0.05\)). Data are Means \(\pm\) SE. \(n=3\).  
mixed forest had the highest MBC, MBN and MBP; the same result was observed for BR (Figure 4). However, the microbial respiratory quotient (qCO\({}_{2}\)) was reduced after farmland was converted to grasslands, shrubs, forests and mixed forests (Figure 4).