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. [ABSTRACT FROM AUTHOR]