Partitioning water source and sinking process of a groundwater-dependent desert plant community

Desert plant community is often structured in two distinct layers of woody and herbaceous plants. Partitioning its water source and sinking process remains a key uncertainty in this water-limited ecosystem. Our aims are to partition the evapotranspiration (ET) components into water loss from bare soil, shrub, and herbaceous plants; estimate the contributions of groundwater to ET and shrub layer transpiration (T (shrub)); and determine the major drivers of ET components in a groundwater-dependent desert plant community in Central Asia. Eddy covariance, static chambers, and micro-lysimeters were used to measure ET and its components (transpiration and evaporation). Oxygen stable isotope and IsoSource model were used to determine the water source of dominant shrubs (Haloxylon ammodendron). The seasonal pattern of transpiration (T) for the herbaceous layer (T (herb)) differed markedly from that for T (shrub). T (herb) reached the maximum values at the beginning of the growing season, and then decreased to nearly zero at the middle and end of the growing seasons. Conversely, T (shurb) were able to maintain throughout the growing season due to the deep root access to groundwater. In total, T (shrub), T (herb), and evaporation (E) were 70, 16, and 82 mm year(-1), they account for 42, 9, and 49% of total ET during 2014. Most of the groundwater was consumed by T (shrub) (51 mm year(-1)), accounted for 73% of T (shrub). The contribution of groundwater to ET was 60 mm year(-1), representing more than 35% of total ET during 2014. The seasonal dynamics of T (shrub), T (herb), and E were shaped by different drivers: T (shrub): air temperature; T (herb): soil water content and herbaceous plant cover; E: net radiation and precipitation. This study demonstrated that a better understanding of the source and sinking process of ET is crucial for predicting hydrological response under ongoing and projected climatic change scenarios in a groundwater-dependent desert plant community.