Carbon and nitrogen accumulation mehcamnisms in forested ecosystem and its estimation

在这项研究中，我们使用稳定的和放射性的碳同位素和土壤分级方法，在日本的一个由C_4草原改建的C_3针叶林中。枯枝落叶层与枯枝落叶层下土壤有机碳的δ^&lt；13&gt；C值相差5‰或更大，这主要归因于枯枝落叶层的快速分解和前C4植被碳的保存。大部分土壤有机碳Δ^&lt；14&gt；C值在整个土壤剖面中均为负值，表明土壤剖面中的有机碳大多为顽固性有机碳，且保存时间较长。只有表面沙子的值略为正值。这些结果表明，大部分新输入的碳在土壤表面被消耗。这些土壤对新输入碳的保存能力较差是土壤碳恢复缓慢的原因之一。从植被恢复的土壤有机质来看，虽然表层土壤有机质随森林经营发生了变化，但土壤碳没有显著变化。经过40年的重新增长，它达到了平台期。这一数值与顶极林的有机质积累量基本一致。认为经过40年的森林恢复生长，森林生态系统的碳、氮积累量已达到潜在积累量。

In this study, we used stable and radioactive C isotopes with soil fractionation methods in a C_3 coniferous plantation converted from C_4 grassland, in Japan. The difference in δ^<13>C 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 C_4 vegetation. Most SOC Δ^<14>C 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. From the results of soil organic matter with vegetation re-growth, there was no significant change in soil C, although the surface soil organic matter changed with forest management. It reached the plateau after 40 years of re-growth. The value was almost similar to the accumulated organic matter in the climax forest. It is considered that carbon and nitrogen accumulation in the forested ecosystem reaches the potential amount after 40 years of forest re-growth.