Development of an automatic chamber system for long-term measurements of CO₂ flux from roots

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.