Temporal Variation and Hysteresis of Soil Respiration and Sap Flow of Pinus densiflora in a Cool Temperate Forest, Japan

Soil respiration (R-s) consists of autotrophic (R-a) and heterotrophic (R-h) respiration, and the metabolic responses of R-a and R-h are supposedly affected by environmental factors. Our hypothesis was that the contribution of R-a and R-h would be affected by seasons. To characterize seasonal patterns of R-s, sap flow (as an indicator of photosynthetic activity), and environmental factors, we continuously measured temporal variation in R-s using an automated opening and closing chamber system in a cool temperate forest. R-s had counterclockwise hysteresis (R-s: spring < autumn) with soil temperature at a depth of 5 cm. Daily maximum R-s had a significant positive relationship with daily maximum sap flow over three seasons, and daily maximum sap flow was lower in autumn than in spring (R-a: spring > autumn). The amount of leaf litterfall increased significantly from August to October; the high R-s in autumn would be due to an increase in R-h (R-h: spring < autumn). These results suggest that R-a contributes more in spring than in autumn, and the contribution of R-h is high from summer through autumn.