量化退耕还林后土壤碳变化

为了评价退耕还长白落叶松对土壤碳的影响，该文以中国东北地区的敦化市为例，选择了7个退耕后演替的不同时间序列的长白落叶松样地，及其附近的250年生原始林作为土壤长期碳汇潜力的一个参照，通过采集矿质土壤样品，并测定生物量碳、凋落物碳，研究长白落叶松第1个轮伐期间土壤碳量和质的变化．结果表明，退耕后12年碳密度降低到最小量75.87 Mg/hm2，然后逐渐恢复； 在退耕21年的时候，土壤有机碳恢复到农田的水平，即84.28Mg/hm2．21年后土壤碳密度出现净积累．造林后33年，土壤碳的增加和减少与生物量碳的累积相比是比较小的，而长期来看（250年），土壤碳库占整个生态系统碳库的63.4%．这种情况表明，肥沃的土壤退耕还林后，长期来看是一个可观的碳汇．颗粒态有机质是土壤有机质中对土地利用变化比较敏感的指标．在0 ～30 cm土层中, 长白落叶松林地和原始林粗颗粒态有机质分别是耕地的2.7和3.4倍，颗粒态碳在土壤总碳中的分配比例是增加的，表明退耕还林后土壤质量在好转． 

Quantifying the soil carbon changes following the afforestation of former arableland

In this study, in order to assess the impacts of the first cycle of Larix olgensis afforestation on soil organic carbon, the authors used Dunhua City in northeast China as a case region to investigate the soil carbon in seven Larix olgensis stands during different afforestation periods, with an adjacent 250-year-old natural forest as the control for the possible long term soil carbon storing in northeast China. Mineral soil was sampled and the carbon contained in forest biomass and forest floors was measured to explore the qualitative as well as quantitative changes of soil carbon. Results showed that soil carbon decreased to a minimum level of 75.87 Mg/hm² in the first 12 years and then gradually recovered. In the 21st year after afforestation, the soil organic carbon density of forests rose to a level as high as that in the former cropland, ie 84.28 Mg/hm² Thereafter, the soil carbon started to accumulate. Within the short time span of 33 years, the amounts of carbon lost or gained by soil were much smaller than those accumulated in forest biomass. The soil carbon accounts for 63.4% of the ecosystem carbon stock in the 250-year-old afforested stand, suggesting that nutrient rich afforestation soils may serve as the potential sinks for carbon in long term. Particulate organic matter (POM) was a sensitive index to reflect the soil quality. In the 0-30 cm soil layer, the percentages of coarse POM for the L. olgensis and natural forests were 2.7 and 3.4 times as high as that for the cropland. The proportion of particulate organic carbon in the total soil carbon increased, which indicates an improvement of the soil quality after afforestation.