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Abstract: Horqin Sandy Land is a seriously desertified and an ecologically fragile region of China. Soil degradation and desertification in this region are the result of several decades of overgrazing, non-manure cropping with short fallow, and arbitrary land use and management. We investigated whether the afforestation of active sand dunes with Mongolian pine (Pinus sylvestris var. mongolica Litv.) enhances the carbon (C) and nitrogen (N) storages and the overall soil quality. We compared soil physico-chemical properties, and C and N storages in the total and light fraction soil organic matter of active sand dunes, and of 25- and 35-year-old plantations. Soil water holding capacity, fine particle content and nutrients were significantly higher in plantations than in active sand dunes, with greater improvements occurring in the top 5cm than in the 5–15cm layer of the soil profile. Soil C and total N storages were 6.1 and 3.7 folds in 25-year-old, and 10.2 and 5.3 folds in 35-year-old plantations compared to active sand dunes, respectively. Carbon and N storages in the light fraction were 20.9 and 15.8 folds in 25-year-old, and 36.1 and 25.0 folds in 35-year-old plantations, respectively, relative to active sand dunes. The light fraction played an important role in soil C sequestration and its amount is an indicator of the effects of afforestation on C storage in sandy soil. The upper 15cm of the soil profile in the 35-year-old plantations of Mongolian pine has the capacity to sequester significant amount of C in the region, potentially offsetting part of the carbon that has been lost due to desertification over the past century in the Horqin Sandy Land. Our results conclude that afforestation with Mongolian pine has had positive impacts on soil quality and has increased the capacity for soil C sequestration in semi-arid degraded areas. [Copyright &y& Elsevier]