The role of increasing soil water-stable aggregates with diameter > 0.25mm by vegetation restoration in enhancement of soil organic carbon in the Loess Plateau

In this study, we investigated the changes in soil water stable aggregates of 05cm surface and their organic carbon contents induced by different restoration vegetation types (grass, shrub and tree) at 3 sites including Suide, Wuqi, Yichuan in Shaanxi province on the Chinese Loess Plateau. Water stable aggregates with diameters of 2 mm and 20.25 mm and their organic carbon contents (SOC) were significantly increased by all vegetation types and these increases were different among three investigated sites. Compared with farmland, restoration of Pinus tabulaeformis and Caragana in Suide site resulted in an increase of SOC in water stable aggregates of 2 mm and 20.25 mm by 99%153% and 219%350%, respectively. At Wuqi site, Alfalfa and Hippophae respectively increased SOC in water stable aggregates of2 mm and 2 0.25 mm by 28%～30% and 85%～130%, whereas Locust tree did not increase SOC in water stable aggregates of 2 mm but increased SOC by 210% of 2 0.25 mm diameter. At Yichuan site, Pennisetum flaccidum,Bothriochloa ischemum (L.) Keng, Sophora viciifolia and Pinus tabulaeformis respectively increased SOC in water stable aggregates of 2 mm and 2 0.25 mm by 405%932% and 724%1130%. The enhancement of SOC by restoration of vegetation on cultivated slopes is mainly the increase of SOC in soil water-stable aggregates of two diameters 2 mm (514%) and 20.25 mm (470%), but not for other diameters. The increased values of SOC of 2 mm and 2 0.25 mm respectively contributed to 49% and 43% of total SOC increased by vegetation restoration while less than 16% SOC increase in other diameters of water-stable aggregates. These results suggest that the formation of water-stable aggregates of 0.25 mm diameter through stabilization of soil structure by vegetation may play an important role in soil carbon sequestration in the eroding landscapes of the Chinese Loess Plateau.