REGULAR ARTICLE Biodegradation of low molecular weight organic compounds and their contribution to heterotrophic soil respiration in three Japanese forest soils Kazumichi Fujii & Chie Hayakawa & Patrick A. W. Van Hees & Shinya Funakawa & Takashi Kosaki Received: 1 October 2009 / Accepted: 13 April 2010 / Published online: 7 May 2010 # Springer Science+Business Media B.V. 2010 Abstract Low molecular weight (LMW) organic compounds in soil solution could be important substrates for heterotrophic soil respiration. The importance of LMW organic compound mineraliza- tion in heterotrophic soil respiration needs to be confirmed for different types of soils. The concen- trations of LMW organic compounds in soil solution and mineralization kinetics of 14 C-radiolabelled glu- cose, acetate, oxalate and citrate were studied in three Japanese forest soils (Andisol, Spodosol and Incepti- sol) with varying adsorption capacities. Based on those results, the fluxes of LMW organic compound mineralization and their magnitude relative to hetero- trophic soil respiration were quantified. Monosac- charides and organic acids comprised on average 5.9– 11.2% and 0.9–1.4% of dissolved organic carbon in soil solution, respectively. Monosaccharide minerali- zation make up 49–74% of heterotrophic (basal) soil respiration at the soil-profile scale, while organic acid mineralization accounts for between 5% (Andisol) and 47–58% (Spodosol and Inceptisol) of heterotro- phic soil respiration. The mineralization of LMW organic compounds is a substantial fraction of heterotrophic soil respiration regardless of soil type, owing to their rapid and continuous production and consumption. The specific contribution of organic acid mineralization to heterotrophic soil respiration varies depending on soil adsorption capacities, name- ly iron and aluminum oxides. Keywords Adsorption . Dissolved organic carbon . Low molecular weight organic acid . Mineralization . Monosaccharide . Soil respiration Introduction Dissolved organic carbon (DOC) in soil solution consists of high molecular weight (HMW) humic substances and low molecular weight (LMW) organic compounds. LMW organic compounds include mono- and disaccharides, low molecular weight organic acids (LMWOAs), amino acids and amino sugars, and phenolics (Van Hees et al. Plant Soil (2010) 334:475–489 DOI 10.1007/s11104-010-0398-y Responsible Editor: Klaus Butterbach-Bahl. K. Fujii (*) : C. Hayakawa : S. Funakawa Graduate School of Agriculture, Kyoto University, Oiwake-cho, Sakyo-ku, Kyoto 606-8502, Japan e-mail: kazushi@kais.kyoto-u.ac.jp P. A. W. Van Hees Man-Technology-Environment Research Centre, Department of Natural Science, Örebro University, Örebro 701-82, Sweden T. Kosaki Department of Tourism Science, Tokyo Metropolitan University, Tokyo 192-0364, Japan