The carbon budget of coarse woody debris in a temperate broad-leaved secondary forest in Japan

To separate CO₂ efflux from roots (R_r) and soil (R_s), we developed a system to measure R_r continuously. Using this system, seasonal variation in R_r was obtained in a temperate forest in Japan. We measured R_s, CO₂ efflux from mineral soil (R_m) and environmental factors simultaneously, and the characteristic and seasonality of R_r were analysed in comparison with R_s. R_r and R_s showed different responses to soil water content: R_s decreased with decreasing soil water content, whereas R_r peaked at relatively low soil water content. R_r/R_s decreased from 64.8% to 27.3% as soil water content increased from 0.075 to 0.225 cm cm⁻³. The relationship between respiration and temperature appears to change seasonally in response to phenological and biological factors. R_r showed clear seasonal variation as a function of soil temperature. During the growing period, R_r exhibited a higher rate at the same soil temperature than during other periods, which may be due to phenological influences such as fine root dynamics. R_s decreased during the summer despite high soil temperatures. The seasonal peak for R_s occurred earlier than that for soil temperature. R_r/R_s ranged between 25% and 60% over the course of the year. DOI: 10.1111/j.1600-0889.2006.00216.x

Characteristics of CO 2 flux over a forest on complex topography

To assess the effect of changes in organic litter stock on seasonal changes in heterotrophic respiration (R _H), soil respiration (R _S), and total ecosystem respiration (R _E), we measured seasonal changes in leaf litter respiration (R _LL) by the chamber method and estimated the seasonal change in total R _H using the RothC model in a warm-temperate mixed deciduous–evergreen forest in Japan. Both R _E and R _S had seasonal hysteresis and were higher in spring than at the same temperature during autumn. Under warm and humid conditions, the rate of decomposition of newly supplied leaf litter in one year was high (60% loss). Consequently, R _LL and R _H were higher in spring after leaf drop, when more fresh material was available, than in autumn. In this study, 42 and 88% of the difference in R _E and R _S between spring and autumn (soil temperature 16–18°C) could be accounted for by the difference in R _H, respectively, and 71% of the difference in R _H could be accounted for by the difference in R _LL. This study showed that seasonal changes in heterotrophic respiration (R _LL and R _H) could be a major factor in the seasonal hysteresis of R _E and R _S.