Through comparing the concentration and inventory of
soil organic carbon (SOC) and its distribution in soil profiles under
cropland,rangeland,natural secondary forest (brushwood,natural secondary forest dominated by Querces liaotungensis or Populus davidiana) and larch plantations (13,18 and 25 years old Larix principis-rupprechtil),this paper studied the effect of
land use change from natural secondary forest to cropland or rangeland as well as from cropland or rangeland to plantation on SOC storage in the Liupan mountain forest zone.The results showed that the concentration of SOC in 0～110 cm soil layer under cropland and rangeland was 54% and 27% lower than that under natural secondary forest,respectively.The difference of SOC concentration between natural secondary forest and cropland or rangeland was greater in 0～50 cm than in 50～110 cm soil layer,while that between larch plantations and cropland or rangeland was greater in 0～40 cm than in 40～110 cm soil layer.The inventory of SOC in 0～110 cm soil layer under cropland and rangeland was respectively 35% and 14% lower than that under natural secondary forest,while 23% lower under cropland and 4% higher under rangeland than that under larch plantations.The difference of SOC inventory between natural secondary forest and cropland or rangeland was greater in 0～50 cm than in 50～110 cm soil layer,while that between plantations and cropland or rangeland was greater in 0～30 cm than in 30～110 cm soil layer.The decreasing magnitude of SOC storage with soil profile depth under natural secondary forest or larch plantations was greater than that under cropland or rangeland.The above-mentioned facts resulted from the changes of SOC input or output and the distribution of roots in soil.The results indicated that the SOC concentration and inventory would decline (mainly in 0～50 cm soil layer) after converting from natural secondary forest to cropland or rangeland,but increase (mainly in 0～30 cm soil layer) following afforestation on cropland.The SOC concentration would increase but its inventory would not change following afforestation on rangeland,and the distribution of the SOC concentration or inventory in soil profile would change with the change of land use in Liupan mountain forest zone.