The largest carbon pool in forest ecosystems is the soil, and CO2 efflux from the soil surfaces is the main pathway for carbon moving from the terrestrial ecosystem into the atmosphere. It is very important to reveal whether the ability of CO2 absorption in the forest ecosystems would be change or not, if the global warming proceeds. Our study was conducted in a secondary red pine forest at the National Institute for Environmental Studies in Tsukuba in central Japan. We installed multichannel automated open-closed chamber systems and infrared heating system in 2006. We measured heterotrophic respiration rates with warming treatment and no-warming treatment using an infrared gas analyzer (Li-820, Licor Inc.) between 2006 and 2010. We evaluated how heterotrophic respiration (Rh) will respond to long term changes in temperature and soil water contents by soil warming treatment.

The maximum value of monthly mean Rh (2006-2010) with warming treatment was 10.68 μmol CO2 m-2 s-1 in August 2006 and the minimum value was 1.87 μmol CO2 m-2 s-1 in January 2010. The maximum value of monthly mean Rh with no-warming treatment was 9.94 μmol CO2 m-2 s-1 in August 2006 and the minimum value was 1.66 μmol CO2 m-2 s-1 in February 2009.The soil warming treatment enhanced the heterotrophic respiration rate by 4.1% during five years. In this research, heterotrophic respiration rates were tended to decrease year by year.