Effects of land-use changes on organic carbon in bulk soil and associated physical fractions in China's Horqin Sandy Grassland

The Horqin Sandy Grassland is one of the most seriously desertified areas in China’s agro-pastoral ecotone due to its fragile ecology, combined with improper and unsustainable land management. We investigated organic carbon changes in bulk soil(0 to 5 cm), light fraction of soil organic matter, and soil particle-size fractions induced by land-use and cover type changes. The results indicated that total soil organic carbon(SOC) storage decreased by 121 g/m2 with the conversion of grassland into farmland for 30 years, and increased by 261 g/m2 with the conversion of grassland into plantation for 30 years. Total SOC storage decreased by 157 g/m2 as a result of severe grassland desertification due to long-term continuous livestock grazing, whereas total SOC increased by 111 g/m2 following the practice of grazing exclusion(16 years) in desertified areas. Changes in land-use and cover type also show great effects on carbon storage in soil physical fractions.