Water-use characteristics of two dominant plant species in different community types in the Mu Us Desert

Shrubs are pioneer species for ecological restoration in drylands and can promote the growth of herbaceous plants. Knowledge of the water-use characteristics of these revegetated species in different community types is crucial for understanding interspecific and intraspecific interactions and guiding ecological restoration; however, few studies have focused on this process. In this study, we explored the water sources and root distribution of plants in three community types in the Mu Us Desert: a mixed community including a shrub species Artemisia ordosica and a grass species Leymus secalinus, a pure A. ordosica community, and a pure L. secalinus community. We measured the delta 18O of the plant xylem and soil water within 100 cm of the soil surface and surveyed the root biomass distribution. The main water source for both A. ordosica and L. secalinus in mixed communities was from the shallow soil layer (0-20 cm) and it overlapped most of the time. When soil moisture in the shallow soil layer was low, L. secalinus still used water from the shallow soil layer, whereas A. ordosica mainly used water from the dry deep soil layer (60-100 cm). The water sources for A. ordosica were significantly different among different communities. In contrast, L. secalinus had similar water sources in different communities. We also found that the root biomass of shrubs was significantly lower in mixed communities than in pure communities. Moreover, when available soil water increased, the root biomass of grasses increased significantly, whereas that of shrubs did not significantly change. These results suggest grasses have an advantage over shrubs in competing for water and this may lead to the exclusion of shrubs from the community, and grasses dominated community. Our study can be used as a reference for assessing the persistence of shrub species to guide future ecological restoration.