In the arid and semi-arid regions of the Loess Plateau, seasonal freezing and thawing influence soil water movement, and water movement directly influences vegetation growth. However, currently, research with regard to freezing and thawing processes under various vegetation types and the mechanism of soil water movement is lacking. Therefore, the present study explored soil water migration characteristics of two typical vegetation types (arbor land [AL] and shrub land [SL]) on the Loess Plateau during seasonal freezing and thawing processes using bare land (BL) as a control. We used field measured data for hourly soil temperature (ST) and soil water content (SWC) at a depth of 100 cm below the soil surface from November 2017 to March 2018. Freezing and thawing process was divided into three stages based on ST change (initial freezing period, stable freezing period, and thawing period). The results revealed that: 1) the maximum freezing depth of AL and SL was 60 cm, which was 30 cm less than that of BL. The freezing date of each soil layer in BL was the earliest and average ST value was the lowest. BL had the highest degree of freezing. The freezing of all soil layers in AL occurred at a later date than that of SL. ST and the minimum soil freezing temperatures were higher than those of SL, and the capacity of AL to resist freezing was higher; 2) the SWCs in AL and BL at depths of 0–10 cm and 10–30 cm decreased, whereas SWCs of AL and BL at a depth of 60 cm increased by 152% and 146%, respectively. The SWCs of SL at soil depths of 0–10 cm, 10–30 cm, and 30–60 cm increased by 46.3%, 78.4% and 205%, respectively. The amount and distribution of soil moisture in SL were optimum when compared to those of AL and BL. The results of the present study could provide a scientific basis for vegetation restoration in arid and semi-arid areas of the Loess Plateau.

中文翻译：

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黄土高原季节性冻融区不同植被类型下土壤冻融和水分输送特征

在黄土高原干旱半干旱地区，季节性冻融影响土壤水分运动，水分运动直接影响植被生长。然而，目前缺乏对不同植被类型下的冻融过程和土壤水分运动机制的研究。因此，本研究以裸地（BL）为对照，探讨了黄土高原季节性冻融过程中两种典型植被类型（乔木地[AL]和灌木地[SL]）的土壤水分迁移特征。我们使用2017年11月至2018年3月土壤表面以下100 cm深度的每小时土壤温度（ST）和土壤含水量（SWC）的现场测量数据。 根据ST变化将冻融过程分为三个阶段（最初的冻结期，稳定冻结期和解冻期）。结果表明：1）AL和SL的最大冻结深度为60 cm，比BL小30 cm。BL各土层的冻结日期最早，平均ST值最低。BL 的冻结程度最高。AL 中所有土层的冻结发生时间晚于 SL。ST和最低土壤冻结温度高于SL，AL抗冻能力更高；2) AL和BL在0-10 cm和10-30 cm深度的SWCs减少，而AL和BL在60 cm深度的SWCs分别增加了152%和146%。SL 在 0-10 cm、10-30 cm 和 30-60 cm 土壤深度处的 SWCs 分别增加了 46.3%、78.4% 和 205%。与 AL 和 BL 相比，SL 中土壤水分的数量和分布是最佳的。本研究结果可为黄土高原干旱半干旱区植被恢复提供科学依据。