六道沟小流域地形序列土壤碳剖面分布特征及影响因素

为了更好地理解黄土高原植被恢复与生态重建过程对土壤碳循环过程的影响,研究选取位于黄土高原六道沟小流域的典型土壤地形序列(东北坡NE序列,西坡W序列),分析了不同坡向间及同一坡向内随植被类型变化土壤有机碳和无机碳的剖面分布特征及其影响因素。结果表明:六道沟小流域地形序列土壤有机碳含量在0—50cm土层内随土层深度增加而显著降低,50cm土层以下基本趋于稳定,且剖面上层(0—50cm)有机碳含量显著高于剖面下层(50—200cm,p0.05),但在同一深度土层(0—50,50—200,0—200cm)不同坡向林地和草地土壤有机碳平均含量均没有显著差异(p0.05)。与有机碳相比,无机碳含量相对较高并且主要在剖面下部(50cm以下)不同深度土层富集。NE序列林地和草地剖面无机碳平均含量接近(p0.05),而W序列林地剖面无机碳平均含量显著高于草地(p0.05);不同坡向草地剖面无机碳平均含量无显著差异(p0.05),但不同坡向林地剖面无机碳平均含量表现为W序列显著高于NE序列(p0.05)。0—50cm土层有机碳含量与pH、容重和土壤含水量均呈极显著负相关关系,而与土壤总孔隙度呈极显著正相关关系;50—150cm土层无机碳含量与pH和土壤总孔隙度均呈极显著负相关关系,而与容重、黏粒含量和土壤含水量均呈极显著正相关关系。NE序列和W序列2 m土体总碳密度相当,分别为15.2~47.4kg/m~2和18.3~51.3kg/m~2,其中无机碳密度占78%~94%,1—2m土层总碳密度占2m土体总碳密度的35%~74%。若只考虑土壤有机碳库或只考虑浅层1m土壤碳库,六道沟小流域2m土体总碳储量平均将被低估88%和51%。

Distribution Characteristics and Influencing Factors of Soil Carbon Profile Along Toposequences in Liudaogou Watershed

In order to understand the effects of vegetation restoration and ecological restoration process on soil carbon cycling,the profile distribution of soil organic and inorganic carbon under different slopes and vegetation types along two toposequences of Liudaogou watershed on the Loess Plateau (China) were investigated,and the profile distribution characteristics and the influencing factors of soil organic carbon and inorganic carbon among different slopes and among different vegetation types on the same slope were analyzed.The typical toposequences were located in the northeast slope (NE sequence) and west slope (W sequence) of the Liudaogou watershed,respectively.The results showed that soil organic carbon content decreased significantly with increasing of soil depth within 0-50 cm soil layer,and then remained relatively constant in the soil layer deeper than 50 cm,and the organic carbon content of the 0-50 cm soil layer was significantly higher than those of the 50-200 cm soil layers (p＜0.05).However,in the same soil depth (0-50,50-200 or 0-200 cm),there was no significant difference on the mean organic carbon content under either forestlands or grasslands among different slopes (p ＜ 0.05).Compared with organic carbon,soil inorganic carbon content was relatively high,and mainly enriched in the different soil layers deeper than 50 cm.In the NE sequence,the mean inorganic carbon contents were comparable in the forestland and the grassland (p＞0.05).In contrast,in the W sequence the mean inorganic carbon content of the forestland was significantly higher than that of the grassland (p＜0.05);there was no significant difference on the mean inorganic carbon content of the grasslands among different slopes (p＞0.05),while the mean inorganic carbon content of the forestland in the W sequence was higher than that in the NE sequence (p＜0.05).Organic carbon content in the 0-50 cm soil layer was significantly negatively correlated with pH,bulk density and soil water content,but was significantly positively correlated with soil total porosity;inorganic carbon content in the 50-150 cm soil layer was significantly negatively correlated with pH and total soil porosity,but was significantly positively correlated with bulk density,clay content and soil water content.Soil carbon densities within 0-2 m profile were 15.2～ 47.4 kg/m2 and 18.3～51.3 kg/m2 in the NE sequence and W sequence,respectively,in which inorganic carbon density accounted for 78％～94％.Total carbon density of 1-2 m soil layer were 35％74～％ of the total carbon density of 0-2 m soil profile.Our study indicated that neglecting inorganic carbon or neglecting deep soil carbon (1-2 m) would lead to underestimation of soil carbon stock by 88％ and 51％,respectively.