Identifying sizes and turnover times of rapidly-cycling soil organic carbon pools by thin-layered soil incubations and C measurements

Moriya, Koichi*; Koarashi, Jun   ; Atarashi-Andoh, Mariko  ; Moriizumi, Jun*; Yamazawa, Hiromi*; Hirai, Keizo*

Soil organic carbon (SOC) decomposition is an important component of the global carbon cycle, because SOC is the largest carbon reservoir in terrestrial ecosystems and a small change in the CO flux from SOC may lead to a large change in atmospheric CO concentration. For the accurate estimation of SOC decomposition, it is important to identify sizes and turnover times of SOC pools. We tried to estimate three SOC pools (active, slow and resistant) with different mean residence times (MRTs) by a combination of soil incubation and C analysis. The active SOC held 1% of the total SOC with MRTs of 1-3 weeks. The slow SOC accounted for 20-50% of the total with MRTs of 1 to 17 years. The active and slow SOC contributed greatly to the total CO production, and the primary source shifted from the active to the slow one. Our result shows the importance of quantifying the dynamics of rapidly-cycling SOC pools to accurately predicting the response of soils to climate change.