## Results
### Inter-Correlations among SOCD, SR, Q10 and TT  
Figure 4 shows that SOCD is weakly but significantly related to SR and TT (\(R^{2}\) > 0.14, \(p\) < 0.001) but not with Q10 (\(R^{2}\) = 0.00, \(p\) > 0.05), indicating that SOC accumulation was mainly due to an increase in TT. Soil basal respiration depended on SOCD and TT but had no relation with Q10, whereas TT was negatively related with SR and Q10 (Figure 4E,F). These results suggested SOC accumulation during urbanization might result from an increase in TT. \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Types**} & \multicolumn{3}{c}{**Human Disturbance Time-Related Gradients**} & \multicolumn{3}{c}{**Ring Road-Related Gradients**} \\ \cline{2-11}  & **114 Year** & **60 Years** & **24 Years** & **10 Years** & **0 Year** & **1 st** & **2 nd** & **3 rd** & **4 th** & **5 th** \\ \hline \multicolumn{11}{c}{Forest Types} \\ \hline RF & 0.25 & 0.28 & 0.32 & 0.39 & 0.26 & 0.29 & 0.16 & 0.36 & 0.36 & 0.28 \\ AF & 0.42 & 0.33 & 0.35 & 0.37 & 0.21 & 0.19 & 0.35 & 0.4 & 0.4 & 0.18 \\ LF & 0.33 * & 0.38 * & 0.28 * & 0.24 * & 0.13 * & 0.52 * & 0.45 * & 0.24 * & 0.08 * & 0.16 * \\ PF & 0 & 0.01 & 0.05 & 0 & 0.04 & 0 & 0.04 & 0 & 0.12 & 0.38 \\ EF & 0 & 0 & 0 & 0 & 0.36 & 0 & 0 & 0 & 0.04 & 0 \\ \hline \multicolumn{11}{c}{Compositional differences} \\ \hline Betulaceae & 0.08 & 0.04 & 0.04 & 0.15 & 0.11 & 0.10 & 0.07 & 0.04 & 0.06 & 0.13 \\ Acceraceae & 0.08 & 0.04 & 0.09 & 0.05 & 0.02 & 0.03 & 0.07 & 0.05 & 0.02 & 0.04 \\ Rosaceae & 0.08 & 0.24 & 0.28 & 0.32 & 0.15 & 0.06 & 0.22 & 0.40 & 0.28 & 0.11 \\ Pinaceae & 0.17 & 0.26 & 0.26 & 0.15 & 0.18 & 0.39 & 0.29 & 0.11 & 0.28 & 0.16 \\ Salicaceae & 0.25 & 0.28 & 0.19 & 0.22 & 0.39 & 0.26 & 0.22 & 0.21 & 0.26 & 0.42 \\ Ulmaceae & 0.17 & 0.01 & 0.07 & 0 & 0.08 & 0.06 & 0.04 & 0.07 & 0.02 & 0.05 \\ Other spp. & 0.17 & 0.12 & 0.07 & 0.12 & 0.08 & 0.10 & 0.09 & 0.12 & 0.08 & 0.09 \\ Conifer & 0.17 & 0.24 & 0.25 & 0.15 & 0.18 & 0.35 & 0.29 & 0.11 & 0.26 & 0.16 \\ Broadleaf & 0.83 & 0.76 & 0.75 & 0.85 & 0.82 & 0.65 & 0.71 & 0.89 & 0.74 & 0.84 \\ \hline \multicolumn{11}{c}{Soil properties} \\ \hline BD (g/cm\({}^{3}\)) & 1.38 & 1.39 & 1.36 & 1.39 & 1.38 & 1.37 & 1.38 & 1.38 & 1.36 & 1.38 \\ pH & 8.03 & 7.84 & 7.73 & 7.99 & 7.76 & 7.62 & 7.69 & 7.93 & 8.02 & 7.82 \\ EC (μs/cm) & 182.9 * & 145.0 * & 112.6 * & 116.8 * & 99.2 * & 165.0 * & 131.6 * & 125.3 * & 123.0 * & 95.9 * \\ \hline \multicolumn{11}{c}{Tree size properties} \\ \hline DBH (cm) & 17.06 & 16.73 & 15.65 & 17.15 & 16.95 & 19.49 & 16.22 & 14.74 & 16.01 & 17.85 \\ TH (m) & 8.84 & 7.98 & 7.33 & 7.89 & 7.97 & 10.17 & 7.28 & 7.02 & 6.93 & 8.38 \\ HUB (m) & 2.12 & 2.63 & 2.21 & 2.04 & 2.54 & 3.17 & 2.55 & 2.00 & 2.01 & 2.64 \\ CS (m\({}^{2}\)) & 20.31 & 23.83 & 20.84 & 28.83 & 20.3 & 25.67 & 22.51 & 21.76 & 21.62 & 22.8 \\ \hline \multicolumn{11}{c}{* indicates marked linear changes of this parameter at urban–rural gradients. Forest types are: RF, roadside forest; AF, affiliated forest; LF, landscape and relaxation forest; EF, ecological and public welfare forest; and PF, production and management forest. Other abbreviations are: BD, soil bulk density; EC, soil electrical conductivity; DBH, tree diameter at breast height; TH, tree height; HUB, tree height under branch; and CS, tree crown size.} \\ \end{tabular}
\end{table} 
Table 2: Urban–rural gradient changes in forest type proportion, tree composition proportion, soil properties and tree sizes, in Changchun city, China. Forest Types, Composition, Tree Sizes and Soil Properties and their Contributions to the Urban-Rural SOC Patterns  
Pearson correlations were used to determine correlation coefficients for various factors (Table 3). The forest types and soil properties were significantly related with SOCD and Q\({}_{10}\) variation, whereas SR was significantly associated with soil properties and tree size. TT was significantly related with forest type and species composition proportion as well as soil properties.