Using water isotopes to analyze water uptake during vegetation succession on abandoned cropland on the Loess Plateau, China

The Chinese government implemented the largest environmental recovery plan in the 1990s, the Grain for Green Project, on the Loess Plateau to prevent soil erosion. Extensive areas of cultivated land were abandoned and then gradually restored with communities of native vegetation. Little is known, however, about the successional development of these communities and their strategies of water use. We collected soil and root samples from four vegetation communities at different stages of succession (Artemisia capillaris, A. sacrorum, Bothriochloa ischaemwn and Lespedeza davurica) in the dry and wet seasons of 2015 in the Wangmaogou watershed of the Wuding River. Both the root systems and soil-water contents tended to increase with successional development and fluctuated with changes of the dry and wet seasons. Isotopic analysis indicated that the thawing of winter snow during the dry season in April provided sufficient soil water. The vegetation communities only used the water in the 0-20 cm soil layer during the early successional stage. This range increased to 0-100 cm as the succession developed, with strong seasonal variation; water was accessed from deeper soil during the dry season, and water was accessed from shallower soil during the wet season. Antecedent rainfall, soil-water content and root distribution strongly influenced the use of water in all four vegetation communities. In the process of restoration and succession of vegetation communities, the behavior characteristics and water absorption strategies of the root system are the important theoretical basis for optimizing the selection of species and accelerating the speed of ecological restoration in Chinese Loess Plateau.