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Koarashi, Jun; Atarashi-Andoh, Mariko; Ishizuka, Shigehiro*; Kadono, Atsunobu*; Moriya, Koichi*; Nakanishi, Takahiro
no journal, ,
Soils are the largest carbon (C) reservoir in terrestrial ecosystems, and may act as both a source and sink of atmospheric CO
in response to climate change. Identifying the sizes and turnover times of soil organic carbon (SOC) pools is a crucial step to predicting the fate of soil C. Here, we used a 
C-based approach to quantitatively understand how much and how long Japanese forest soils store C in their surface horizons. We collected soil samples from deciduous forests, separated the samples into SOC fractions, and then determined their C ratios to estimate mean residence times (MRTs). The MRTs ranged from years to millennia, which revealed a different distribution of MRTs between the soils. We found that the total amount of C correlated positively with the size of the SOC pools cycling on time scales of 
100 years, but poorly with the size of faster-cycling pools. The results suggest that the soils with higher C stocks do not necessarily have higher potential for CO emission.
C and C signaturesNakanishi, Takahiro; Koarashi, Jun; Atarashi-Andoh, Mariko; Hirai, Keizo*
no journal, ,
Dissolved organic carbon (DOC) is an important constituent in forest soils, because it affects soil formation and transport of heavy metals, is a source of C for microbes, and contributes to soil organic carbon (SOC) accumulation. In this study, we measured 
C and 
C in water extractable organic carbon (WEOC) to investigate the dynamics of DOC at Appi, a cool temperate deciduous forest in Japan. The C values of WEOC were slightly higher than those of SOC. Such enrichment in C indicated that WEOC production, which was coupled with the microbial activity, mainly used a C-enriched SOC fraction (including sugars, amino acids, etc.) of the total SOC. Indeed, hydrophilic fractions were enriched in C compared to the total WEOC. Hydrophilic fractions are considered more biologically available for decomposition. The result of C indicated that WEOC consists mainly of C-enriched, labile, hydrophilic organic materials with faster turnover times (several decades).
C measurementsMoriya, Koichi*; Koarashi, Jun; Atarashi-Andoh, Mariko; Moriizumi, Jun*; Yamazawa, Hiromi*; Hirai, Keizo*
no journal, ,
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.
respired from a beech forest floorAtarashi-Andoh, Mariko; Koarashi, Jun; Moriya, Koichi; Nakanishi, Takahiro; Ishizuka, Shigehiro*; Hirai, Keizo*
no journal, ,
no abstracts in English