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.