How long do Japanese forest soils store carbon in their surface horizons?

Koarashi, Jun   ; Atarashi-Andoh, Mariko  ; Ishizuka, Shigehiro*; Kadono, Atsunobu*; Moriya, Koichi*; Nakanishi, Takahiro   

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.