Abstract: Vegetation type and terrain are the main factors affecting the vertical distribution of soil organic carbon (SOC) on regional scale. In this study, the effects of vegetation type and terrain on the vertical distribution of SOC were examined based on field investigation, sample collection and lab analysis in four abandoned farmlands (woodland, shrub land, mixed forest, and grassland) in the Caijiachuan watershed of western Shanxi Province. The results showed that: (1) The SOC contents decreased gradually with the increase of soil depth in the 0-200 cm soil layer. The variation coefficients of each soil layer ranged from 30%-52%. (2) Vegetation type affected the SOC contents significantly to the soil depth of 120 cm, and the SOC contents of the whole profile presented as mixed forest > woodland > shrub land > grassland. (3) Terrain factors showed significant effects on the vertical distribution of SOC. The altitude, slope gradient, slope position and slope aspect had significant effects on the SOC at the depth of 60, 40, 80 and 60 cm respectively. The SOC contents decreased gradually with the increase of slope gradient and slope position, the SOC contents were higher on shady slopes than on sunny slopes, and were higher at the latitude of 1100-1200 m and 1000-1100 m than at >1200 m and <1000 m. (4) The variance component analysis showed that vegetation type, terrain and soil layer explained 66.10%, 22.02% and 11.88% variability of SOC, respectively. Our results had theoretical and methodological significances for evaluating the carbon sequestration benefits of the abandoned farmlands in the loess area.

Key words: greenhouse soil, glomalin-related soil protein, soil nutrient, aggregate, soil enzyme activity