Distribution of light fraction organic carbon under different land use types in the deep soil layer of hilly regions of the Loess Plateau,  China

Taking the Robinia pseudoacacia woodlands, Caragana korshinskii shrublands, abandoned croplands, and slope croplands in hilly regions of the Loess Plateau as study objects, we investigated the contents and distribution ratios of soil light fraction organic carbon (LFOC) in the deep soil layer(100-400 cm) under different land use types by using the method of relative density fractionation with the shallow soil layer(0-100 cm) as the control. The results show that there are significantly declining trends in the content and distribution ratio of soil light fraction organic carbon along with the increase of soil depth under the studied land use types. The contents of soil light fraction organic carbon range from 0.09 to 1.76 g/kg, while the distribution ratios of soil light fraction organic carbon range from 4.19% to 32.24%. Under the three land use types, the contents and distribution ratios of soil light fraction organic carbon in the subdeep soil（100-200 cm) and deep soil(200-400 cm) of that in the shallow layer(0-100 cm) range from 12.4% to 39.8%, 28.7% to 66.2%, respectively. The declining rates of the soil light fraction organic carbon contents and distribution ratios are Robinia pseudoacacia woodlands＞abandoned croplands＞Caragana korshinskii shrublands＞slope croplands. The contents and distribution ratios of soil light fraction organic carbon in the same soil layer among the three land use types are different. The contents and distribution ratios of soil light fraction organic carbon both are forestlands＞abandoned croplands＞slope lands in these three layers. Both the contents and distribution ratios of soil light fraction organic carbon are increased after the implementation of the Grain for Green project, while those in the sub-deep and deep soils of those in the shallow layer are reduced. Compared with the shallow soil layer, the stability of deep soil organic carbon is enhanced respectively in the process of revegetation.