Abstract Understanding how different tree species consume soil water is critical for land management, especially in areas with limited water resources. This study examined the soil water consumption characteristics of two exotic tree species—economic forest apple tree (Malus pumila) and ecological forest black locust (Robinia pseudoacacia)—and the effect of soil desiccation on plant transpiration in the 2018 growing season in a semi-arid region of the Loess Plateau. We investigated root distribution and deep soil water content in the vertical soil profile and used hydrogen and oxygen stable isotopes to identify the contribution of water to transpiration in shallow (0–2 m) and deep (>2 m) soil. We also measured sap flow changes using thermal dissipation probes during the growing season. The apple orchard had a maximum rooting depth of about 16 m, with a deep soil water deficit of about 771 mm. The corresponding figures for the black locust forest were about 25 m and 1926 mm. In previous years, the apple trees consumed 51.4 mm yr–1 of deep soil water and black locust consumed 120.4 mm yr–1. In the 2018 growing season, soil water content varied from 0–200 cm depth, with no significant changes beyond 200 cm in either species. Shallow soil water contributed, on average, 68.1% and 80.9% to transpiration in the apple orchard and black locust forest, respectively, and both they had a similar amount of transpiration during the growing season. These results indicate that rapid deep soil desiccation leads to a lack of sustainable root water uptake in deep soil, and the dominance of transpiration by precipitation in this region. This study increased our understanding on how intensive water extraction from deep soil affects tree transpiration, which is significant for sustainable afforestation in the Loess Plateau and other regions with similar hydrogeology.

中文翻译：

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黄土高原经济林（Malus pumila）和生态林（Robinia pseudoacacia）在深部土壤缺水约15年后的蒸腾作用以降水为主

摘要 了解不同树种如何消耗土壤水对于土地管理至关重要，尤其是在水资源有限的地区。本研究考察了经济林苹果树 (Malus pumila) 和生态林刺槐 (Robinia pseudoacacia) 两种外来树种的土壤耗水特征，以及 2018 年半生长季土壤干燥对植物蒸腾作用的影响。黄土高原干旱区。我们调查了垂直土壤剖面中的根系分布和深层土壤含水量，并使用氢和氧稳定同位素来确定水对浅层 (0–2 m) 和深层 (>2 m) 土壤中蒸腾作用的贡献。我们还使用散热探针在生长季节测量了树液流量的变化。苹果园的最大生根深度约为 16 m，深层土壤水分亏缺约 771 毫米。刺槐林的相应数字约为 25 m 和 1926 mm。前几年，苹果树消耗了 51.4 mm yr-1 的深层土壤水，而刺槐消耗了 120.4 mm yr-1。在 2018 年的生长季节，土壤含水量在 0-200 厘米深度范围内变化，超过 200 厘米的任何一个物种都没有显着变化。在苹果园和刺槐林中，浅层土壤水对蒸腾作用的贡献率分别为68.1%和80.9%，两者在生长季节的蒸腾量相似。这些结果表明，深层土壤快速干燥导致深层土壤缺乏可持续的根系吸水，并且该地区降水蒸腾作用占主导地位。