The soil is an important carbon reservoir in the ecosystem, which stores about 2 times as the atmosphere and 2.6 times as the plant biomass (Schimel 1995). However it is difficult to estimate precisely the amount of carbon pool in the soil and there have still been many unknown factors to be investigated.
Most of previous works about the carbon cycle has been concerned with steady state of the climax phase ecosystem and only a little investigation have been done for the changing ecosystem with the plant succession. While it is known that the soil organic matter is accumulated with the progress of the primary succession (Tezuka 1961), the carbon dynamics in the secondary succession in which the soil exists from the beginning has not been clear.
The first purpose of this study is to investigate two different phases of ongoing secondary plant succession, grassland and forest from the plant ecology standpoint in order to estimate the variation of soil carbon dynamics during the secondary plant succession.
While stable isotopic ratio 13C/12C has been used as a useful tool for the investigation of carbon dynamics, studies using radiocarbon 14C came to be reported recently with the recent generalization of AMS method. 14C-AMS requires very small amount of sample so that it is advantageous in studying narrow site and heterogeneous field as in Japan. Thus the second purpose of this study is to examine the validity of radiocarbon as a tracer for the soil carbon dynamics of grassland and forest in Japan. To do this we already have soil samples which were obtained twice, in the year 1980s and 2001, from Japanese pampas grassland and Japanese red pine forest in Sugadaira Heights, Nagano Prefecture, Japan.
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