Soil Organic Carbon Contents of Larix principis-rupprechtii Plantations in the Southern Part of Liupan Mountains | 六盘山南部华北落叶松人工林土壤有机碳含量

Chinese. 研究造林措施和林龄对宁夏六盘山南部不同坡向华北落叶松人工林土壤有机碳的影响。结果表明：造林后,各坡向的土壤有机碳含量均呈现先下降、后上升的变化过程,其对造林干扰的敏感程度随土层加深而减弱;在阳坡半阳坡,造林10年后的幼龄林0～45cm土层土壤有机碳密度（96.33t・hm. 2）仍低于灌丛（122.12t・hm. 2）,造林20年后的中龄林（189.27t・hm. 2）已高于灌丛,说明土壤碳库已得到恢复;在阴坡半阴坡,幼龄林和中龄林的土壤碳密度分别为192.37和222.03t・hm. 2,均低于天然次生林（256.64t・hm. 2）,说明造林20年后土壤碳库仍未恢复;阳坡半阳坡林地在造林后第8年0～45cm土层有机碳含量降至最低,相对阳坡灌丛（32.13g・kg-1）的降幅为3.72g・kg-1,需在造林后第16年才能恢复到造林前的灌丛水平;阴坡半阴坡林地在造林后第16年降至最低,相对阴坡次生林（66.30g・kg-1）的降幅为22.77g・kg-1,需在造林后第32年才能恢复到造林前次生林水平;阴坡造林后,其土壤有机碳比阳坡损失量大,损失期长,恢复较慢,但阴坡土壤碳库的绝对值在任何林龄阶段都高于阳坡,说明阴坡森林土壤的碳储存能力高于阳坡;在阳坡半阳坡灌丛采用扰动较弱的稀植造林时,造林后第10年0～45cm土层有机碳含量平均为31.05g・kg-1,虽仍低于灌丛（35.55g・kg-1）,但却远高于扰动较强的全面整地后常规密度造林（23.17g・kg-1）。

English. In this paper,we investigated influences of plantation measures and forest ages on soil organic carbon（SOC） of Larix principis-rupprechtii plantations with different slope aspects in the Southern Liupan Mountains was studied.The results showed that the SOC content on all aspects presented the same trend of firstly decreasing after tree-planting and then recovering.The SOC sensibility to environment variation,such as plantation disturbance,decreased with increasing soil depth.The time required for restoring the SOC density in the soil layers of 0-45 cm to the level of pre-afforestation varied with site conditions.On the sunny and semi-sunny aspects,the SOC density（96.33 t・hm. 2） in 0-45 cm soil layers of a 10 years young plantation was still lower than that of the shrub land（122.12 t・hm. 2）;however,the SOC density（189.27 t・hm. 2） of the 20 years middle-aged plantation after afforestation was higher than that of the shrub land,indicating that the SOC was restored before this forest age.On the shady and semi-shady aspects,the SOC density of the young and middle-aged plantations was 192.37 and 222.03 t・hm. 2,respectively,and both were lower than that of the naturally regenerated forests（256.64 t・hm. 2）,indicating that the SOC was still not restored after 20 years afforestation.Based on the statistical analysis of the investigated SOC content in the soil layers of 0-45 cm,the SOC content of 0-45 cm soil layers would decrease to the lowest point after 8 years afforestation on the sunny/semi-sunny aspects,with the decrease of 3.72 g・kg-1 compared to the control of shrub land（32.13 g・kg-1） on sunny aspect,and the fully recovering of SOC to the pre-plantation level would require 16 years after plantation.On the shady/semi-shady aspects,the SOC content would decrease to the lowest point after 16 years plantation,with the decrease of 22.77 g・kg-1 compared to the control of secondary forests（66.30 g・kg-1）,and the fully recovering of SOC to the pre-plantation level would require 32 years after plantation.The SOC on shady aspects after plantation had a bigger loss,longer decreasing period and slower recovering rate than those on the sunny aspect.However,the absolute values of the SOC pool on the shady aspects were always higher than that on the shady aspects at any forest age,suggesting that the capacity of carbon sequestration at shady aspects was higher than that of sunny aspects.Our study demonstrated that the planting disturbance was able to affect the change of SOC pool.The mean SOC content in the 0-45 cm soil layers on sunny/semi-sunny aspect was 31.05 g・kg-1 after 10 years plantation if the trees were planted with sparse spacing,considerably higher than that（23.17 g・kg-1） of forests planted with normal density,however still lower than that of the control of shrub land（35.55 g・kg-1）.