Partitioning of respiratory CO 2 fluxes in a managed C 3 turfgrass field Yoshiko KOSUGI *, Masayuki I TOH**, Takashi MATSUBARA ***, Satoru T AKANASHI ****, Ken’ichi OSAKA *****, Yoko MIZOTA ***, Masako D ANNOURA *, Tetsuya SHIMAMURA ******, and Naoki MAKITA * *Graduate School of Agriculture, Kyoto University, Kyoto 606–8502, Japan ***Center for Ecological Research, Kyoto University, Otsu, Shiga, 520–2113, Japan ***Obayashi Corporation Technical Research Institute, Kiyose, Tokyo 204–8558, Japan ****Forestry and Forest Products Research Institute, Tsukuba, Ibaraki 305–8687, Japan *****International Research Center for River Basin Environment, University of Yamanashi, Kofu, Yamanashi 400–8501, Japan ******Faculty of Agriculture, Ehime University, Matsuyama, Ehime 790–8566, Japan Abstract To evaluate the respiration and temperature dependence of each component of a managed C3 cool- season turfgrass (Kentucky bluegrass, Poa pratensis ) field and to elucidate the characteristics of the carbon budget, respiratory CO2 fluxes from leaves, non-assimilatory organs, and decomposition (soil heterotrophic respiration) were measured using a closed dynamic chamber method. Analysis of tem- perature dependence using the Arrhenius function was performed for partitioning of the components of ecosystem respiration. The activation energy for respiration was 40,200 J mol –1 for non-assimilatory organs, 41,600 J mol –1 for leaves, and 69,800 J mol –1 for heterotrophic respiration. Total ecosystem respiration at 25 ℃ was 9.0 μmol m –2 s –1 in June 2006 and 8.2 μmol m –2 s –1 in August 2007. Leaf, non-assimilatory organ, and heterotrophic respiration at 25℃ was 1.7 (19 ％), 4.8 (53 ％), and 2.5 (28 ％) μmol m –2 s –1 , respectively, in June 2006, and 1.8 (22 ％), 4.1 (50％), and 2.3 (28 ％) μmol m –2 s –1 , re- spectively, in August 2007. A large proportion of non-assimilatory organ respiration coincided with the non-assimilatory organ biomass. At the study site, soil respiration as the sum of non-assimilatory organ and heterotrophic respiration formed 78-81 ％ of the total ecosystem respiration, and the proportion of autotrophic respiration (non-assimilatory organ respiration) to total soil respiration was 64-66 ％. The total ecosystem respiration and soil respiration were very large in comparison with the values reported for other ecosystems. Key words: Activation energy, Autotrophic respiration, Ecosystem respiration, Heterotrophic respira- tion, Temperature dependence. Received; October 1, 2009. Accepted; February 26, 2010. 1. Introduction For the planning and maintenance of C3 cool-season turfgrass fields in warm climates and transitional regions, evaluating the balance between temperature and plant carbon uptake (photosynthesis) and loss (respiration) is essential. The balance is evaluated as the difference between total carbon assimilation from photosynthesis and carbon loss from plant respiration (i.e., from leaves, stems, and roots). A few studies have examined the depression of canopy photosynthesis and mass decline of C3 turfgrass at high temperatures (Xu and Huang, 2000a, b, 2001a, b, 2003; Huang and Liu, 2003; Su et al ., 2007) and the partitioning of net photosynthesis, total ecosystem respiration, and soil respiration in a C3 turfgrass field using chamber measurements (Bremer and Han, 2005). However, partitioning of the respiration rate for each component Full Paper J. Agric. Meteorol. (農業気象) 66 (3): 151–161, 2010 151