Characteristics of soil respiration temperature sensitivity in a Pinus/Betula mixed forest during periods of rising and falling temperatures under the Japanese monsoon climate

We studied temperature sensitivity characteristics of soil respiration during periods of rising and falling temperatureswithin a common temperature range. We measured soil respiration continuously through two periods (a period of fallingtemperature, from August 7, 2003 to October 13, 2003; and a period of rising temperature from May 2, 2004 to July 2,2004) using an open-top chamber technique. A clear exponential relationship was observed between soil temperatureand soil respiration rate during both periods. However, the effects of soil water content were not significant, becausethe humid monsoon climate prevented soil drought, which would otherwise have limited soil respiration. We analyzedtemperature sensitivity using the Q10 value and Rref (reference respiration at the average temperature for the observationperiod) and found that these values tended to be higher during the period of rising temperature than during theperiod of falling temperature. In the absence of an effect on soil water content, several other factors could explain thisphenomenon. Here, we discuss the factors that control temperature sensitivity of soil respiration during periods of risingand falling temperature, such as root respiration, root growth, root exudates, and litter supply. We also discuss how thecontribution of these factors may vary due to different growth states or due to the effects of the previous season, despitea similar temperature range.