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FOREST, RANGE & WILDLAND SOILS

Possible Mechanisms Leading to a Delay in Carbon Stock Recovery after Land Use Change

^a Laboratory of Silviculture, Division of Forest and Biomaterials Science, Graduate School of Agriculture, Kyoto Univ., Kyoto 606-8502, Japan
^b Field Science Education and Research Center, Kyoto Univ., Kyoto 606-8502, Japan
^c Dep. of Environmental Science & Technology, Interdisciplinary Graduate School of Science and Engineering, Tokyo Inst. of Technology, Yokohama 226-8502, Japan
^d Tokyo Univ. of Agriculture and Technology, Saiwai-cho 3-5-8, Fuchu-city, Tokyo, 183-8509, Japan

^* Corresponding author (hiroarai{at}kais.kyoto-u.ac.jp).

Changes in land use sometimes lead to soil C loss, and a long time may be required for the C stock to recover to initial levels. Thus, it is important to evaluate the mechanisms related to accumulation of newly input C following land use changes. In this study, we sought to determine the signature of newly input C in the soil profile after land use change. We used stable and radioactive C isotopes with soil fractionation methods in a C₃ coniferous plantation converted from C₄ grassland in Japan. The difference in ¹³C values between the surface litter and the soil organic carbon (SOC) below the litter was 5 or greater; this large isotopic difference was attributed to rapid decomposition in the litter layer and preservation of C derived from the previous C₄ vegetation. Most SOC ¹⁴C values were negative throughout the soil profile, suggesting that most of the SOC in the soil profile was recalcitrant and had been preserved for a long time. Only the surface sand values were slightly positive. These results suggest that most newly input C is consumed at the soil surface. The low ability of these soils to preserve newly input C is one factor in the slow recovery of soil C.

Abbreviations: SOC, soil organic carbon