宣威市退耕还林柳杉林地土壤有机碳含量及活性组分的林龄变化

Variation in the Content of Soil Organic Carbon and Its Labile Fractions among Different Age of Cryptomeria fortumei Plantation Afforested by the Grain for Green Program in Xuanwei Municipality of Southwest China

【目的】探讨云贵高原地区土壤有机碳含量及其活性组分在退耕还林后的变化,为退耕还林后的土壤碳储量变化评价和碳汇管理提供科学依据。【方法】在云南省宣威市选择耕地对照和不同退耕还林年数(4,8,12年生)的柳杉人工林地,在不同土层(0~20,20~40和40~60 cm)采集土壤并收集枯落物和细根样品,测定土壤有机碳及其活性组分含量、土壤密度、土壤全氮含量、枯落物现存量和细根生物量。【结果】与耕地相比,退耕还林4,8和12年生时林地0~60 cm土层土壤有机碳含量分别下降20.07%,19.29%和11.52%,即退耕还林初期土壤有机碳含量显著下降,在退耕还林4年后开始逐渐回升,但在12年后仍未恢复到耕地水平;土壤高活性有机碳含量以造林前的耕地最高(4.46 g·kg^(-1)),4年生时最低(2.67 g·kg^(-1));土壤次高活性有机碳含量以8年生时最高(12.03 g·kg^(-1),4年生时最低(4.61 g·kg^(-1));土壤活性有机碳含量以8年生时最高(20.94 g·kg^(-1)),12年生时最低(9.12 g·kg^(-1));土壤有机碳含量及其活性组分含量均随土层加深而减小,且存在显著的土层差异(P<0.05),有机碳含量的最小值(11.14 g·kg^(-1))出现在8年生40~60 cm土层;各林龄柳杉林地0~60 cm土层有机碳含量及其高活性有机碳、次高活性有机碳与土壤全氮含量的相关系数分别为0.894,0.756和0.755,均极显著正相关,与土壤密度的相关系数为-0.664,显著负相关。【结论】退耕还林柳杉林地0~60 cm土层有机碳含量及其活性组分含量随林龄增加先降后升,造林年数和林下枯落物量是影响土壤有机碳含量及其活性组分含量的重要因子,今后在森林碳汇管理中需大力推行封山育林,延长林分林龄,尽量保留林下枯落物。

【Objective】To provide scientific basis for evaluating the soil carbon stock and its management in afforested soils,we investigated the changes in soil organic carbon and its labile fractions after afforestation by the grain for green program.【Method】Cryptomeria fortumei plantation respectively 4,8,and 12 years after planting by the grain for green Program and a farmland without trees as the control were chosen in Xuanwei Municipality,Yunnan Province.Soil,litter and fine roots were collected at different soil layers（0-20,20-40 and 40-60 cm） from the selected plantations and the control plot.Soil organic carbon content and its labile fractions,soil densities,soil nitrogen,as well as litter and fine root biomass were analyzed.【Result】Compared with the farmland,the content of soil organic carbon in the 0-60 cm layer deceased by 20.07%,19.29%,and 11.52%,respectively for 4,8 and 12 years of age,indicating that the soil organic carbon content significantly decreased in the early 4 years and then gradually increased thereafter,but not increased to thelevel in the farmland at the 12 th year after planting.For the highest labile fraction of the soil organic carbon the maximum value was 4.46 g·kg^-1 before planting,and the minimum was 2.67 g·kg^-1 at the 4th year after planting;for the second highest labile fraction,the maximum was 12.03 g·kg^-1 at the 8th year after planting and the minimum was 4.61 g·kg^-1 at the 4th year after planting;for the least labile fraction the maximum was 20.94 g·kg^-1 at the 8th year after planting and the minimum was 9.12 g·kg^-1 at the 12 th year.The contents of both soil organic carbon and its labile components decreased along with the depth of soil layer,and there were significant differences（P〈0.05） among different soil layers;the minimum content（11.14 g·kg^-1） of soil organic carbon was found in the soil layer of 40-60 cm at the 8th year.The correlation coefficients of the soil organic carbon,the highest labile fraction,and the second highest labile fraction with the total soil nitrogen were 0.894,0.756 and 0.755,respectively,which were all significantly positive.The coefficient of soil organic carbon with soil density was-0.664,indicating a significantly negative correlation.【Conclusion】The soil organic carbon and its labile fractions in the 0-60 cm soil layer showed a decrease in early years and an increase in later years in Cryptomeria fortumei plantations.The age and the litter content were important factors affecting the changes.We suggest reduce forest logging and retain the forest litter as far as possible in order to have a good management of forest carbon sink.