[M-IS21_28PO1] Biogeochemistry

[MIS21-P17] A study of soil organic matter stabilization using physical fractionation, isotopic, and spectroscopic approaches

*Rota WAGAI¹, Maki ASANO¹, Chie HAYAKAWA¹, Yudzuru INOUE², Masako KAJIURA¹, Shyuntaro HIRADATE¹, Noriko YAMAGUCHI¹, Yoshiyuki INAGAKI³, Masao UCHIDA⁴, Yasuo TAKEICHI⁵, Hiroki SUGA⁶, Muneaki JINNOU⁵, Kanta ONO⁵, Yoshio TAKAHASHI⁶ (1.National Institute for Agro-Environmental Sciences (NIAES), 2.Kyushu University, 3.Forestry and Forest Products Research Institute, 4.National Institute of Environmental Studies (NIES), 5.High Energy Accelerator Research Organization (KEK), 6.Hiroshima University)

Keywords:土壌炭素, 炭素循環, 有機物・鉱物相互作用, 微細形態分析, 固体分析, 同位体分析

Volcanic-ash soil (Andisol) is unique among the world soil types due to the strong physical stability of organo-mineral aggregate structure at micro and submicron scales (Asano and Wagai, 2013, Geoderma) and its high capacity to store organic matter (OM) even in upland surface horizons under warm, moist climate regime where microbial heterotrophic activity is high. Several hypotheses have been proposed to account for these features of Andisol including (i) strong interaction of OM with dissolved metals (Al, Fe) and/or short-range-order (SRO) minerals that are quite abundant in this soil type, and (ii) preservation of recalcitrant compounds such as char. Here we present some highlights from the 3-year project (GR091, NEXT Program, JSPS) examining the mechanisms of soil OM stabilization with a focus on organo-mineral interactions at various spatial and temporal scales using multiple analytical methods and experimental approaches. After careful consideration of the degree of soil aggregate disruption levels, we physically fractionated Andisol surface horizon sample based on particle size and density. Chemical composition of each physical fraction was assessed by elemental analysis, selective dissolution of inorganic phases, and solid-state ¹³C-NMR. The origin and degree of microbial alteration of OM was estimated from C and N stable isotope ratios while the turnover time of C was assessed by radiocarbon measurements. Physical features of soil mineral and organo-mineral aggregate surfaces were characterized by specific surface area (N₂-BET), XPS, and microscopic methods. We also conducted tracer experiments to further assess the residence time of the OM in each density fractions. Based on these results, we will discuss the progression of organo-mineral associations from fresh plant detritus to the aggregates of varying structure and stability for the studied Andisol.