Observed and modeled root water uptake by sand-fixing semi-shrub in response to groundwater

Groundwater plays a pivotal role in regulating water consumptive use within the soil-plant-atmosphere continuum and maintaining sustainable vegetation restoration in arid areas. Nevertheless, the mechanistic understanding of how groundwater influence root distribution patterns and evapotranspiration (ET) dynamics, as well as how it is partitioned into evaporation (E) and transpiration (T), remains incomplete. In this study, we employed four large-scale weighing lysimeters in a 2×2 factorial design (vegetation: Artemisia ordosica vs. bare soil; groundwater: presence vs. absence), complemented by Hydrus-1D simulations to investigate the groundwater effects on ecohydrological processes in the desert ecosystem. From April to August 2024, we analyzed the influence of groundwater (-2.5 m) on plant growth properties, soil water, ET and its partitioning. Findings revealed that the roots of A. ordosica in desert ecosystems with groundwater extended deeper (-3.0 m) than those without groundwater (-2.8 m). The ratios of root area to leaf area of A. ordosica under conditions without and with groundwater were 5.22-15.4 and 30.1-60.5, respectively. The groundwater increased soil water contents in the middle and deep soil layers, while the higher precipitation (31 mm d^-1) could influence the soil water contents at depths of 0.8-1.0 m. The performance of the model for the simulated soil water contents, E or ET of the four lysimeters with Hydrus-1D achieves satisfactory results (R² = 0.501-0.726, RMSE = 0.0135-0.590, NSE = 0.438-0.692). The observed mean daily ET of A. ordosica was 2.18 ± 0.0973 and 1.19 ± 0.0685 mm d^-1 for the treatment with and without groundwater. The simulated root water uptake (RWU) was clearly higher for the groundwater treatment (1.15 ± 0.0625 mm d^-1) than for the control (0.548 ± 0.0317 mm d^-1). The RWU:ET ratios of A. ordosica were 52.7 ± 1.58% and 50.1 ± 1.57% with and without groundwater. Redundancy analysis and Pearson correlation showed that the presence of groundwater alleviated the influences of low precipitation, relative humidity, and high air temperature on ET and its partitioning. This study provides robust empirical evidence to help us understand the interactions between groundwater-soil-plant-atmosphere in desert ecosystems. This has significant implications for the sustainable revegetation management practices in arid areas.