## 1 Introduction  
Soil respiration (R\({}_{\mathrm{s}}\)) consists of autotrophic respiration (R\({}_{\mathrm{a}}\)) and heterotrophic respiration (R\({}_{\mathrm{h}}\)), and these components use a combination of different carbon sources [1]. Numerous studies have reported that the seasonal variation in R\({}_{\mathrm{s}}\) mainly has an exponential relationship with soil temperature in temperate and boreal forests (e.g., [2, 3]). Global meta-analysis suggests a significant relationship between R\({}_{\mathrm{s}}\) and air temperature anomaly [4]. However, statistical models indicate that the uncertain response of R\({}_{\mathrm{h}}\) to soil water content, which depends on soil characteristics, would cause a difference of at least 4% in global soil carbon stock [5]. Some studies reported that soil water content is also an essential factor in the seasonal variation in R\({}_{\mathrm{s}}\)[6, 7]. Soil temperature and water content are essential factors in spatial variation in R\({}_{\mathrm{s}}\) in a cool temperate forest [8]. According to the results of a meta-analysis, the contribution of R\({}_{\mathrm{h}}\) to total R\({}_{\mathrm{s}}\) tends to be high in regions with small annual R\({}_{\mathrm{s}}\)-for instance, R\({}_{\mathrm{h}}\)/R\({}_{\mathrm{s}}\) ratios are significantly higher in boreal forests than in temperate forests [9]. The contribution of R\({}_{\mathrm{a}}\) to total R\({}_{\mathrm{s}}\) increases with an increase in total R\({}_{\mathrm{s}}\) in temperate and boreal forests, with an average contribution of 45.8% among forest sites [10, 11]. The response of R\({}_{\mathrm{a}}\) to soil temperature is higher than that of R\({}_{\mathrm{h}}\), and the contribution of R\({}_{\mathrm{a}}\) is 48% in a Japanese larch forest [12]. Some studies note that the seasonal variation in R\({}_{\mathrm{s}}\) and soil temperature has a hysteresis relationship, and clockwise and counterclockwise hysteresis tend to be caused by an accelerated or delayed response of photosynthesis to changes in soil temperature [13]. Seasonal hysteresis of R\({}_{\mathrm{s}}\) with soil temperature is clockwise in forests, and it is even more apparent in grasslands [14]. Clockwise hysteresis means that the response of \(\mathrm{R_{s}}\) to soil temperature is greater during spring-summer than during summer-autumn. Only a few field studies that measured \(\mathrm{R_{s}}\) continuously have reported daily hysteresis of \(\mathrm{R_{s}}\) with soil temperature; clockwise hysteresis has been observed in a temperate forest [7; 14] and in a steppe grassland at high elevation [15]. [PERSON] et al. [16] reported that diurnal hysteresis patterns of \(\mathrm{R_{s}}\) with soil temperature differed in each month. \(\mathrm{R_{a}}\) is CO\({}_{2}\) efflux from roots and the rhizosphere. The relationship between gross primary production (GPP) and \(\mathrm{R_{s}}\) has been revealed by using the eddy covariance method [16; 17], but continuous GPP measurement using this method is difficult at observation sites without flux towers. Sap flow is an indicator of plant photosynthetic activity, and GPP estimated using the eddy covariance method has a positive relationship with canopy transpiration flux measured as sap flow [18]. Sap flow has been measured to understand the transpiration between the atmosphere and soil via various plants-for instance, bamboo [19], pine tree [20; 21], and Japanese cedar [22]. Some studies have reported that daily variation in sap flow correlates with vapor pressure deficit (VPD) and solar radiation [19; 22]. If \(\mathrm{R_{a}}\) and \(\mathrm{R_{h}}\) have different metabolic responses to the temporal change of environmental factors, the contribution of \(\mathrm{R_{a}}\) and \(\mathrm{R_{h}}\) to \(\mathrm{R_{s}}\) would be affected by season.