Quantitative understanding of the heterogeneity of soil organic carbon degradability for predicting long-term response of soil carbon to warming

Koarashi, Jun   ; Atarashi-Andoh, Mariko  ; Ishizuka, Shigehiro*; Hiradate, Shuntaro*; Kokubu, Yoko   

Microbial decomposition of soil organic carbon (SOC) is an important component of the global carbon (C) cycle, and even a small warming-driven change in the size and decomposition rate of SOC pools could significantly impact the atmospheric CO concentration and thus the global C cycle. A quantitative understanding of heterogeneity of SOC degradability is essential for a reliable prediction of the response of soils to warming. While fast-cycling SOC pools dominate C fluxes from soils, the longer-term response of soils to warming will be largely determined by the sizes and turnover times of slow-cycling SOC pools in the soils, which can hardly be identified by conventional analytical and incubation methods. We attempted to characterize SOC pools with respect to their sizes and specific turnover times in Japanese forest soils, by a combinatorial use of SOC fractionation and C analysis. We represent the soils as a mixture of SOC pools with different turnover times ranging from years to more than a millennium, and on the basis of this representation and simple model calculations, we show the potential importance of slow-cycling SOC pools with turnover times of several decades to 200 years for the prediction of positive feedback to climate change over the next century.