## 4 Discussion  
The results revealed the counterclockwise hysteresis of the seasonal \(\mathrm{R_{s}}\) with the change of soil temperature (Figure 2), namely, \(\mathrm{R_{a}}\) or \(\mathrm{R_{h}}\) to \(\mathrm{R_{s}}\) was higher in autumn than in spring at the same soil temperature. A comparison of the hysteresis of \(\mathrm{R_{s}}\) in temperate and boreal forests is shown in Table 1. \(\mathrm{R_{s}}\) tended to have a clockwise direction in warmer forests (but also in two cooler forests [7; 29]) and counterclockwise direction in cooler forests. In one study of clockwise direction reported by [PERSON] et al. [7], soil water content decreased from summer to autumn, and therefore \(\mathrm{R_{s}}\) was higher in spring than in autumn. The study by [PERSON] et al. [29] and the present study were conducted in the same forest but reported different results. We cannot clearly explain why the hysteresis of \(\mathrm{R_{s}}\) had opposite directions in the same study area. However, maximum \(\mathrm{R_{s}}\) reported by [PERSON] et al. [29] (about 600 mg CO\({}_{2}\) m\({}^{-2}\) h\({}^{-1}\)) was lower than in our chamber 1 (by 50%; 1200 CO\({}_{2}\) m\({}^{-2}\) h\({}^{-1}\)) and chamber 2 (by 33%; 800 mg CO\({}_{2}\) m\({}^{-2}\) h\({}^{-1}\)). Our findings suggest that the contribution of \(\mathrm{R_{a}}\) could be higher in spring than in autumn; if so, the contribution of \(\mathrm{R_{a}}\) reported by [PERSON] et al. [29] could be higher than in the present study. [PERSON] et al. [13] suggested that counterclockwise hysteresis is caused by a delay of photosynthetic response to soil temperature. In other words, root respiration could be higher from summer to autumn than in spring. In the present study, the daily maximum sap flow rate on sunny days was significantly higher in spring than in autumn (Figure 5), and the daily maximum sap flow was positively correlated with the daily maximum of \(\mathrm{R_{s}}\) (Figure 6a). [PERSON] et al. [30] reported that \(\mathrm{R_{a}}\) has no positive relationship with root temperature. As soil is warmer in the underlayer than at the surface in autumn in cooler forests [16], the contribution of \(\mathrm{R_{h}}\) would become high in autumn. The direction of \(\mathrm{R_{s}}\) hysteresis in the present study was opposite to that in [PERSON] et al. [29] at the same study site. Spatial variation in \(\mathrm{R_{s}}\) was high, the coefficient of variation of daily summed \(\mathrm{R_{s}}\) varied from 25% to 28%, and its variation was similar to that of soil water content at 121 points in a 1-ha site in a mature beech forest [8]. The response of \(\mathrm{R_{s}}\) to environmental factors differs under the canopy and in the gap in a deciduous forest [26]. Continuous measurements of \(\mathrm{R_{s}}\) in the present study were conducted within 1 m\({}^{2}\); the seasonal response of \(\mathrm{R_{s}}\) could differ at each point. Therefore, spatial and temporal variation in \(\mathrm{R_{s}}\) and their response to environmental factors are important to understanding the soil carbon dynamics in forest ecosystems. Using the trenching method, [PERSON] et al. [31] found that the soil temperature response of \(\mathrm{R_{h}}\) is higher than that of \(\mathrm{R_{a}}\) in a broad-leaved secondary forest. The trenching method allows \(\mathrm{R_{a}}\) and \(\mathrm{R_{h}}\) to be physically separated [3; 33; 32], and some studies have separated not only \(\mathrm{R_{h}}\) but also soil organic matter respiration [12] and mycorrhizal respira  
Figure 7: Relationship between sap flow and vapor pressure deficit (VPD) in (**a**) spring, (**b**) summer, and (**c**) autumn. tion [12; 34]. The contribution of \(\mathrm{R_{a}}\) is 45.8% among forest sites around the world [10; 11]. The contribution of \(\mathrm{R_{h}}\) in Japanese forests tends to be higher than that of \(\mathrm{R_{a}}\): it is reportedly 52% [12] and 79% [33] in deciduous forests and 81.5% in a larch forest [3]. In red pine forests, the contribution of \(\mathrm{R_{h}}\) varies from 52% in winter to 80% in summer [35].