【目的】通过分析中国南水北调中线工程水源地较大空间尺度土壤有机碳密度(SOCD)的空间分布及驱动因素,为该区域的土地资源合理利用及土壤有机碳(SOC)管理提供科学依据。【方法】在考虑海拔、土壤类型、土地利用等空间因素的基础上布设样地,通过野外取样和室内分析,借助GIS研究区域土壤有机碳密度空间分布格局,利用地理探测器模型分析各影响因子对土壤有机碳密度的解释力及各因子之间相互作用程度的差异,判定影响研究区SOCD空间分布的主要驱动因子,揭示其空间差异及随海拔、土壤类型、土地利用及森林类型的变化规律。【结果】①南水北调中线工程水源地0~20 cm与≥20~40 cm土层的SOCD分别为4.18和2.67 kg/m²,其中0~20 cm土层SOCD比全国平均水平(2.67 kg/m²)高出56.55%。②SOCD呈现南北林区高、中间农田和草地低的格局,SOCD大于10 kg/m²的集中在海拔≥1 000~2 000 m的林地,小于1 kg/m²的集中在海拔<500 m的草地。在海拔上,SOCD随海拔梯度升高先增大后减小,0~20 cm与≥20~40 cm土层SOCD均在海拔≥1 500~2 000 m出现峰值(7.32 kg/m²,4.94 kg/m²);在土壤类型上,SOCD最大的是石灰(岩)土,最小的是褐土,黄棕壤和棕壤在0~20 cm土层SOC储量最高,分别为2.005 Pg和0.815 Pg,二者占总储量的72.83%;在土地利用类型上,林地和农田是主要的土地利用方式,0~20 cm与≥20~40 cm林地土层SOCD分别为4.87 kg/m²和3.05 kg/m²,农田分别为2.75 kg/m²和2.00 kg/m²(比林地分别下降77.09%和52.50%);林地碳储量占87.48%,农田占12.02%。③对SOCD空间分布解释力较大的是海拔(0.25)和土地利用(0.20),其次是土壤黏粒(0.11)。不同驱动因子在交互作用下的解释力明显高于单因素的解释力。【结论】海拔和土地利用是影响南水北调中线工程水源地SOCD空间格局的主导因子,不同驱动因子交互后呈现双因子协同增强效应。农田SOCD明显低于林地,因此,应加强生态工程建设,进行林地保护和植被恢复,提高该区域土壤碳固存能力。

【Objective】The aim of analyzing the spatial distribution characteristics and driving factors of soil organic carbon density on a large spatial scale in the water source area of the Middle Route of China South-to-North Water Diversion Project is to reveal its spatial differences and the changes with the altitude, soil types, land use, and forest types. This work should provide a scientific basis for the rational utilization of land resources and soil organic carbon (SOC) management in the area. The spatial distribution and driving factors of soil organic carbon density (SOCD) were explored to provide a scientific basis for the accurate assessment of the ecosystem carbon cycle in the climate transition zone.【Method】Based on a comprehensive assessment of spatial factors such as the elevation, soil types, and land use, the spatial variations of SOCD in this region were evaluated by the field sampling and indoor analysis with the help of a geographic information system (GIS). In addition, the main driving factors affecting the spatial distribution of SOCD in the study area were determined by analyzing the explanatory power of various influencing factors on soil organic carbon density and the difference in the degree of interaction among various factors using the geographic detector model. 【Result】(1)The results showed that the average SOCD in 0-20 cm and ≥20-40 cm soil layers was 4.18 kg/m² and 2.67 kg/m² respectively, in which the SOCD of 0-20 cm soil layer was 56.55% higher than the national average level (2.67 kg/m²).(2)Over the entire region, the SOCD was higher in forests in the northern and southern areas and lower in farmlands and grasslands in the middle area. The soil organic carbon density greater than 10 kg/m² is concentrated in the forest land with an altitude of ≥1 500-2 000 m, and less than 1 kg/m² is concentrated in grasslands with altitudes <500 m. The SOCD first increased and then decreased with an increasing elevation. The SOCD of 0-20 cm and ≥20-40 cm soil layers showed peak values (7.32 kg/m² and 4.94 kg/m²) at an altitude of ≥1 500-2 000 m. In terms of soil types, the average SOCD of limestone soil is the greatest and that of cinnamon soils is the smallest. The SOCD storage of yellow-brown earths and brown earths in the 0-20 cm soil layer was the highest, 2.005 Pg and 0.815 Pg, respectively, accounting for 72.83% of the total storage. In terms of land-use types, the forest and farmland were the main land-use types. The SOCD of 0-20 cm and ≥20-40 cm soil layers in the forest land were 4.87 kg/m² and 3.05 kg/m², respectively, and that of farmlands were 2.75 kg/m² and 2.00 kg/m², respectively. These levels were 77.09% and 52.50% lower than that of the forest land, and the SOC storage of the forest land accounted for 87.48% of the total C storage, followed by farmlands (12.02%).(3)The most powerful explanation for the spatial distribution of SOCD was the altitude (0.25) and land use (0.20), followed by soil clay (0.11). The explanatory power of the different driving factors under interaction was significantly higher than that of a single factor. 【Conclusion】The altitude and land use were the main driving factors affecting the spatial patterns of SOCD in this region. After the interaction of different driving factors, there was a synergistic effect of the two factors. The SOCD of farmlands was significantly lower than that of the forest land. Therefore, the ecological engineering construction in the study area should be strengthened, the forest protection and vegetation restoration should be carried out, and the soil carbon storage capacity of the water source in the Middle Route of China South-to-North Water Diversion Project should be improved.