## 5 Conclusions  
To verify our hypothesis that the contributions of \(\mathrm{R_{a}}\) and \(\mathrm{R_{h}}\) to \(\mathrm{R_{s}}\) are affected by season, we continuously measured \(\mathrm{R_{s}}\), sap flow (as an indicator of photosynthetic activity), and environmental factors using automatic measurement systems in a cool temperate forest, Japan. The relationship between \(\mathrm{R_{s}}\) and soil temperature at a depth of 5 cm showed seasonal hysteresis; \(\mathrm{R_{s}}\) tended to be higher in autumn than in spring at the same soil temperature. Daily maximum sap flow was lower in autumn than in spring. Soil water content was higher in spring than in autumn, indicating that the contribution of \(\mathrm{R_{a}}\) could be higher in spring than in autumn. The amount of leaf litterfall increased significantly from August to October, and we concluded that the high \(\mathrm{R_{s}}\) in autumn was likely due to an increase in \(\mathrm{R_{h}}\). Moreover, soil is warmer in the underlayer than at the surface in autumn in cooler forests, and thus the contribution of \(\mathrm{R_{h}}\) would become high in autumn. However, seasonal measurements of \(\mathrm{R_{h}}\) are difficult, and we need more continuous data to understand the contribution of \(\mathrm{R_{a}}\) and \(\mathrm{R_{h}}\) to \(\mathrm{R_{s}}\).  
[PERSON] planned and performed the experiments, analyzed the data, and wrote the paper; [PERSON] analyzed the data; [PERSON] and M.H. performed the experiments and contributed material tools. All the authors worked on editing and revising the manuscript. All authors have read and agreed to the published version of the manuscript.  
This work was supported by JSPS KAKENHI Grant Number JP 21H05318; Mountain Science Center, University of Tsukuba; and River Basin Research Center, Gifu University (2017-F-005).  
**Institutional Review Board Statement**: Not applicable.  
**Informed Consent Statement**: Not applicable.  
**Data Availability Statement**: Not applicable.  
\begin{table}
\begin{tabular}{l l l l l l l l} \hline \hline
**Direction of \(\mathrm{R_{s}}\)** & **Dominant** & **Forest** & \begin{tabular}{l} **Depth of Soil** \\ **Temperature** \\ **Measurement (cm)** \\ \end{tabular} & **Forest Age** & \
\begin{tabular}{l} **Annual Air** \\ **Temperature** \\ **(°C)** \\ \end{tabular} &
\begin{tabular}{l} **Annual** \\ **Precipitation** \\ **(mm yr\({}^{-1}\))** \\ \end{tabular} & **References** \\ \hline Clockwise & _Populus trentuloides_ & MF & 2 * & 81 & 0.3 & 456 & [7] \\ Clockwise & _Quercus kelloggii_ & MF & 8 * & No data & 10.3 & 507 & [14] \\ Clockwise & _Quercus serntata_ & MF & 5 * & 30 & 15.5 & 1388 & [38] \\ Clockwise & _Pinus dessiflora_ & MF & 0 *, 5 *, 10 * & 40 & 6.7 * & 1132 * & [29] \\ Clockwise & _Chameocarpis obtusa_ & PT & 2 & 50 & 13.4 & 1595 & [16] \\ Counterclockwise & _Pinus tabuliformis_ & PT & 10 & 4 & 10.8 & 454 & [39] \\ Counterclockwise & _Pinus splestris_ & MF & 5 & 70 & 5.5 & 527 & [40] \\ Counterclockwise & _Quercus robur_ & PT & 2 & 65 & 9.8 & 750 & [41] \\ Counterclockwise & _Cryptomeria japonica_ & PT & 5 & 2–3 & 10.6 & 1734 & [42] \\ Counterclockwise & _Pinus dessiflora_ & MF & 5 & 55 & 6.8 & 1086 & This study \\ \hline \hline \end{tabular}  
* Clockwise: \(\mathrm{R_{s}}\) in spring \(>\mathrm{R_{s}}\) in autumn, counterclockwise: \(\mathrm{R_{s}}\) in spring \(<\mathrm{R_{s}}\) in autumn, Forest type: MF is mixed forest, PT is plantation.
* daily mean soil temperature, \({}^{\dagger}\) data from Japan Meteorological Agency (2002–2003).  
\end{table}
Table 1: Direction of soil respiration (\(\mathrm{R_{s}}\)) hysteresis in temperate and boreal forest in previous studies.  
**Acknowledgments:** We are grateful to the staff at Sugadaira Research Station, Mountain Science Center, and the University of Tsukuba for supporting our field study and providing climate data.  
**Conflicts of Interest:** The authors declare no conflict of interest.