Ecohydrological processes in water-limited ecosystems are sensitive to deep soil water (DSW), but it remains unclear on how and to what extent deep soil desiccation (DSD) affects these ecohydrological processes, especially during meteorological drought. To address this gap in understanding, we used the Hydrus-2D model — calibrated by continuously observed soil water contents from 0–450 cm soil depth, transpiration (T), and evaporation during the 2018–2021 growing seasons in a dryland apple orchard to determine the ecohydrological response under varying degrees of DSD (> 200 cm) across a range of precipitation levels. The results indicated that deep-rooted apple trees used soil water to a depth of up to 1000 cm, with the proportion of DSW increasing in extremely dry years, causing DSD that inhibited cumulative T and evapotranspiration (ET), which occurred to a greater extent with higher DSD and lower precipitation. Severe deep desiccation and the lack of DSW resources decreased cumulative T by 19.3–23.8% and 37.5–42.5% and ET by 13.0–14.4% and 11.2–23.5%, respectively, across all precipitation amounts in comparison to the cases of no deep desiccation, mild deep desiccation, and moderate deep desiccation. Furthermore, extremely dry years had higher transpiration to evapotranspiration (T/ET) ratios than extremely wet years, independent of the DSD scenario, and precipitation dominated the T/ET change once DSW was unavailable. These findings enhance our understanding of the impacts of the combination of deep soil drought and meteorological drought on ecohydrological processes in water-limited ecosystems and have significant implications for future vegetation dynamics and water resource management in a changing climate.

中文翻译：

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半干旱苹果园深层土壤干燥的生态水文响应


水资源有限的生态系统中的生态水文过程对深层土壤水（DSW）敏感，但目前尚不清楚深层土壤干燥（DSD）如何以及在多大程度上影响这些生态水文过程，特别是在气象干旱期间。为了解决这一理解上的差距，我们使用了 Hydrus-2D 模型，通过连续观测旱地苹果园 2018-2021 年生长季节 0-450 厘米土壤深度的土壤含水量、蒸腾量 (T) 和蒸发量来进行校准，确定不同降水水平范围内 DSD (> 200 cm) 程度下的生态水文响应。结果表明，深根苹果树利用土壤水深度可达1000 cm，极端干旱年份DSW比例增加，导致DSD抑制累积T和蒸散量（ET），发生程度更大。具有较高的 DSD 和较低的降水量。与无深度干燥的情况相比，严重深度干燥和深水资源缺乏使所有降水量的累积 T 分别降低了 19.3-23.8% 和 37.5-42.5%，ET 分别降低了 13.0-14.4% 和 11.2-23.5% 、轻度深度干燥、中度深度干燥。此外，与极端潮湿年份相比，极端干旱年份的蒸腾量与蒸散量 (T/ET) 之比较高，与 DSD 情景无关，一旦 DSW 不可用，降水量将主导 T/ET 变化。这些发现增强了我们对深层土壤干旱和气象干旱相结合对水资源有限的生态系统中生态水文过程的影响的理解，并对气候变化下的未来植被动态和水资源管理具有重大影响。