Abstract Soil water and groundwater are important water resources for vegetation survival and growth in arid and semiarid regions, and their contributions to water use over a whole growth period are difficult to quantify with limited observations. Additionally, the root water uptake (RWU) processes of groundwater-dependent xeric vegetation are specific and aggravate the complexity of these issues. In this paper, Salix is selected to study the interaction among atmosphere, soil water, groundwater, and RWU from the sprout to withered stage based on an observation within the ‘In situ Monitoring Lysimeter System of the Atmosphere-Plant-Unsaturated Zone-Groundwater Continuum’. Two lysimeters with a diameter of 2 m and depths of 1.2 m and 4.2 m were implemented with Salix. The initial water table depth was 0.7 m in case 1 and 2.2 m in case 2. The results show that: Water use of Salix is the main contribution to actual evapotranspiration (ETa), no less than 80%. ETa was 462.75 mm in case 1 with a shallower soil layer and limited groundwater, during the entire growth period, 2016. Contrastively, it was 619.70 mm in case 2 with relatively abundant soil water and groundwater. The soil water and groundwater contribution were 89.6% and 10.4%, 74.3% and 25.7% for both cases. The selective water use by Salix in different soil layers was subject to temporal moisture availability. Salix extended to utilize groundwater in drought period and shifted back to wetter upper layers in case of rainfall. The access to groundwater significantly alleviates water stress, although rainfall replenishment can also play a part. Salix can not only intercept rainfall infiltration in the root zone, but also cause the decrease of water level, implying that the replanting of Salix should be carried out in a reasonable mode to ensure rainfall infiltration and reduce the ineffective loss of groundwater. Our results provide a practical reference for groundwater management and ecology restoration in semiarid desert regions.

中文翻译：

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基于原位观测的半干旱荒漠区可变非饱和带柳属水分利用

摘要 土壤水和地下水是干旱和半干旱地区植被生存和生长的重要水资源，它们对整个生育期用水的贡献难以通过有限的观测进行量化。此外，依赖地下水的干旱植被的根系吸水 (RWU) 过程是特定的，加剧了这些问题的复杂性。在本文中，基于“大气-植物-不饱和区-地下水连续体的原位监测测渗仪系统”的观测，选择柳柳来研究从萌芽到枯萎阶段的大气、土壤水、地下水和 RWU 之间的相互作用'。两个直径为 2 m、深度为 1.2 m 和 4.2 m 的蒸渗仪使用 Salix 实现。案例 1 中的初始地下水位深度为 0.7 m，案例 2 中为 2.2 m。结果表明：柳柳的用水量是对实际蒸散量（ETa）的主要贡献，不低于80%。2016年整个生育期土壤层较浅、地下水有限的情况1的ETa为462.75 mm。相反，土壤水和地下水相对丰富的情况2的ETa为619.70 mm。两种情况下土壤水和地下水的贡献分别为89.6%和10.4%、74.3%和25.7%。Salix 在不同土壤层中的选择性用水受时间水分可用性的影响。Salix 在干旱时期扩展到利用地下水，并在降雨时转移回较湿润的上层。尽管降雨补充也可以发挥作用，但地下水的获取显着缓解了水资源压力。柳柳不仅可以拦截根区降雨入渗，但也造成水位下降，提示柳树的补种要合理进行，以保证降雨入渗，减少地下水的无效流失。研究结果为半干旱荒漠地区地下水管理和生态恢复提供了实践参考。