Understanding the water use characteristics of vegetation is crucial for guiding the rational allocation of water resources and the restoration of sustainable vegetation in natural oases in arid desert areas. To analyze the water use characteristics of Populus euphratica Oliv. and Tamarix chinensis Lour. at different stages of growth in the Daliyabuyi natural pristine oasis in northwestern China, the δ¹⁸O values of plant xylem of 15 sample trees with different sizes per species, potential water sources (i.e., river water, soil water, and groundwater), and the δ¹³C values of plant leaves of sample trees were measured in August 2019 and June 2020. The results show that the δ¹⁸O values of the xylem water of P. euphratica at different growth stages were similar, but water uptake proportions from deep soil water changed in P. euphratica trees at different growth stages between years with (2019) and without (2020) river water. In contrast, the main water source of young T. chinensis shrubs was deep soil water, and those of mature and overmature shrubs were deep soil water and groundwater in 2020. However, the plant leaf water use efficiency (WUE) of the P. euphratica and T. chinensis were higher without river water. Overall, the water uptake proportion from groundwater and the WUE for T. chinensis were higher than those for P. euphratica, and thus, T. chinensis was more dependent on groundwater. This means that vegetation types and growth stages are the essential factors to be considered in ecological restoration management, which can enhance the effectiveness of vegetation restoration strategies.

Beta diversity indicates the species turnover with respect to a particular environmental gradient. It is crucial for understanding biodiversity maintenance mechanisms and for prescribing conservation measures. In this study, we aimed to reveal the drivers of beta diversity patterns in desert hinterland oasis communities by establishing three types of surface water disturbance and groundwater depth gradients. The results indicated that the dominant factor driving the beta diversity pattern within the same gradient shifted from soil organic matter to pH, as groundwater depth became shallower and surface water disturbance increased. Among the different gradients, surface water disturbance can have important effects on communities where original water resource conditions are extremely scarce. Under the premise that all habitats are disturbed by low surface water, differences in groundwater depth dominated the shifts in the community species composition. However, when groundwater depth in each habitat was shallow, surface water disturbance had little effect on the change in species composition. For the two components of beta diversity, the main drivers of species turnover pattern was the unique effects of surface water disturbance and soil environmental differences, and the main driver of species nestedness pattern was the common effect of multiple environmental pressures. The results of this study suggest that increasing the disturbance of surface water in dry areas with the help of river flooding will help in promoting vegetation restoration and alleviating the degradation of oases. They also confirm that surface water and groundwater mutually drive the establishment of desert oasis communities. Equal focus on both factors can contribute to the rational ecological recovery of dryland oases and prevent biodiversity loss.

Understanding the effect of flooding on groundwater quality is imperative for oasis vegetation protection and local ecological environment development. We used geochemical and remote sensing inversion methods to evaluate the effects of flood recharge on the groundwater hydrochemical and geochemical processes in the Daliyaboy Oasis. Groundwater samples were collected from 30 ecological observation wells in the study area before (PRF) and after (POF) the flood. Except for small changes in HCO₃⁻ and K⁺ and a decrease in pH, ion levels were higher POF than PRF, and the water chemistry was essentially unchanged. In the POF groundwater, HCO₃⁻ was correlated with Cl⁻, Na⁺, Mg²⁺, total soluble solids (TDS), and electrical conductivity (EC), but not with SO₄²⁻, Ca²⁺, K⁺, or pH, and was positively correlated with all other variables, while the remaining variables, except for pH, were strongly positively correlated with each other. PRF water chemistry was controlled by silicate and evaporite mineral weathering and evaporation processes, resulting in high groundwater TDS, EC, and a major ion content, while POF major groundwater ions were regulated by mineral weathering and flood recharge. We demonstrated the high accuracy of remote sensing inversion, confirming this as a reliable method for evaluating groundwater chemistry. The results of the study help to reshape and predict the history of the regional hydrogeological environment and hydrogeochemical development, and provide a theoretical basis for assessing the rational use of local water resources and protecting the ecological environment.

Warming and persistent droughts may exacerbate drought stress in water-scarce areas, thereby negatively affecting tree growth. When riparian plants in arid regions experience severe drought stress, they sacrifice non-dominant branches with less competitive sap flow to improve the sap flow of dominant branches and thus ensure strong plant growth. Populus euphratica is one of the most dominant tree species in the riparian forest ecosystems of inland river basins in arid zones and is a reliable indicator of ecological change because of its diversity in growth and environment. To understand the adaptability of P. euphratica to the environment, the relationship between radial growth and meteorological factors, the growth decline and resistance of different heights and components of P. euphratica, as well as the resilience and resilience after recession were investigated. The results indicated that tree-ring width decreased gradually with increasing height and branching class of P. euphratica. Growth decreased at the bottom of the stem earlier than at the middle and top. Temperature, precipitation, and the Palmer drought index contributed to the growth at the bottom of P. euphratica, while precipitation contributed to growth at the top. The decline in the P. euphratica growth change rate was highly synchronized across heights and parts, with relatively high declines at the bottom and top. There were no significant differences in the recovery values for different heights and parts of P. euphratica, but the resistance, resilience, and relative resilience for the bottom and top were significantly lower than those for the other components, indicating vulnerability in the bottom and top of P. euphratica to drought. The relative resilience gradually decreased with the increase in branching class, and that of the secondary lateral branches at different heights was the lowest. In conclusion, the sensitivity of the top and lateral branches of P. euphratica to drought would cause the phenomenon of “breaking its arm” under drought disturbance in the future.