随着我国西部露天煤矿产能持续增加，对原本脆弱的生态环境破坏更加严重，而该地区位于干旱半干旱区，降雨量少，土壤水分含量较低，缺水成为限制该区域生态重建的主要制约因素。因此，深入研究重构土层及植物水分高效利用方法成为该区域生态重建的关键。以西部干旱半干旱煤矿区先锋植物-苜蓿(Medicago sativa L.)为研究对象，通过室内土柱试验筛选出最佳重构土层，并在最佳重构土层的基础上揭示丛枝菌根真菌（AMF）对苜蓿水分利用效应的影响，同时探究了AMF传输水分和对土壤水力特性影响的机制，最后通过野外试验，验证了重构土层和接种AMF对土壤水分保蓄和植物高效用水的影响，为矿区生态重建提供了可行的思路。主要研究结果如下：

（1）为了探究煤矿区排土场适合的重构土层，通过对5种重构土层的土壤蒸渗特征及其对植物生长的研究发现，湿润峰的一维垂向运动均随入渗时间的延长而增加。重构层状土的入渗特征较好，总蒸发量较小，土壤蒸发能力低，蒸发抑制率较高。重构层状土的植物地上和地下生物量比均质砂土高。特别是，地表以下20 - 40 cm为黄土的重构层状土植物地上和地下生物量最高，根长密度、根体积和根表面积在不同土壤深度也最高，并且细根（直径<1 mm）长度也最长。因此，地表以下20 - 40 cm为黄土的重构层状土蒸渗特征较好，并且更有利于植物生长，适合作为西部干旱半干旱煤矿区重构土层的选择。

（2）为了揭示AMF对苜蓿水分利用效应的影响，研究重构土层和接种AMF对不同深度土壤水分和植物根系分布规律。结果表明：重构层状土中20 - 40 cm黄土层内土壤含水量很高(>30%)，并且40 - 100 cm土层的含水量也相对较高(20 - 25%)。不同土壤深度中，重构层状土的根系生物量高于均质土。接种AMF的根系密度高于不接种处理。在不同土壤深度中，接种AMF的根系生物量也显著高于不接种处理，尤其在0 - 20 cm土层中。与不接种相比，接种AMF处理在重构层状土处理和均质土处理中，苜蓿在浅层的水分吸收比例分别降低了12.00%和14.10%。重构层状土和接种AMF处理使苜蓿对浅层土壤水分吸收比例降低，对中层和深层土壤水分吸收比例升高，在干旱半干旱地区能使植物表现出更高的生态可塑性。同时，接种AMF增加植物叶片δ¹³C，促进植物水分利用效率。

（3）为了探究干旱条件下AMF向苜蓿传输水分的机制，通过重氧水（标记¹⁸O）直接跟踪和量化不同水分土壤基质（高水分处理，田间持水量的70%；低水分处理，田间持水量的40%）中AMF对宿主苜蓿的输水过程。发现无论土壤基质处于高水分或者低水分处理，AMF吸收重氧水的苜蓿根、茎、叶和蒸腾水中¹⁸O显著富集，表明AMF可以直接吸收水分并传输给植物根系。在高水分土壤基质中，AMF向苜蓿传输水量为0.26 ± 0.02 mL·d^-1，占苜蓿总蒸腾水的12.32 ± 1.06%。在低水分土壤基质中，AMF向苜蓿传输水量为0.12 ± 0.02 mL·d^-1，占苜蓿总蒸腾水的17.03 ± 1.59%。AMF直接向苜蓿传输水量相比于植物蒸腾需求来说不能被忽略，并且在低水分土壤基质中AMF向苜蓿输送水分的贡献比高水分土壤基质更加重要。

（4）为了探究AMF对土壤水力特性的影响机制，研究了水分条件（低水分处理，田间持水量的40%；高水分处理，田间持水量的70%）和接种AMF水平（接种AMF和不接种AMF）对土壤水力特性（保水性和导水性）的影响。发现接种AMF处理的土壤饱和导水率在低水分和高水分土壤基质中，分别比不接种处理降低16.84%和29.03%。接种AMF处理的土壤毛管孔隙度在低水分和高水分土壤基质中，比不接种AMF处理分别提高了5.04%和10.38%。非毛管孔隙度的变化，与毛管孔隙度恰恰相反。接种AMF处理的土壤水分特征曲线在低水分和高水分土壤基质中，均比相应不接种处理高，表明接种AMF能够改变土壤水分特征曲线，增加土壤持水能力。高水分土壤基质通过影响AMF处理中定殖率、定殖强度和菌丝密度，进而影响土壤水力特性。

（5）为了验证重构土层和接种AMF对土壤水分保蓄和改善植物水分利用策略的效应，通过野外试验，研究重构土层和接种AMF对植物高效用水的影响。发现与均质土相比，重构层状土中植物株高在不接种AMF和接种AMF处理分别提高7.13%和29.11%；植物SPAD值分别提高2.42%和35.19%。重构层状土剖面使得土壤水分和全氮、全磷、全钾含量在20 - 40 cm处显著增加。与均质土相比，重构层状土能够提高植物根系总生物量。接种AMF处理的土壤全氮、全磷、全钾含量在不同深度中均显著低于不接种处理，表明接种AMF增加了苜蓿对土壤养分的利用。与不接种处理相比，接种AMF处理在均质土和重构层状土处理中植物根系总生物量分别提高2.8倍和2.3倍，总的细根长密度分别提高了2倍和1.6倍。通过MixSIAR模型分析了不同处理中苜蓿对不同深度土壤水分的吸收比例，重构层状土和接种AMF均能够有效改变植物水分利用策略，降低植物对0 - 20 cm土壤的水分吸收比例，同时增加对20 - 40 cm和40 - 100 cm土壤层的水分吸收比例。重构层状土剖面和接种AMF联合处理对植物水分利用策略的改善作用更加明显，使苜蓿的主要水源已经转变为20 - 40 cm。这有利于西部干旱半干旱煤矿区植物利用较深层土壤水分，以减少对0 - 20 cm土壤层水分的依赖。

With the continuous increase in production capacity of open-pit coal mines in western China, the damage to the originally fragile ecological environment has become more severe. The area is located in an arid and semi-arid region, with low rainfall and low soil moisture content. Water scarcity has become the main limiting factor for ecological reconstruction in the region. Therefore, in-depth research on the reconstruction of soil layers and efficient utilization of plant water has become the key to ecological reconstruction in this region. Taking Medicago sativa L., a pioneer plant in the arid and semi-arid coal mining area of western China, as the research object, the optimal reconstructed soil layer was screened through indoor soil column experiments. Based on the optimal reconstructed soil layer, the influence of arbuscular mycorrhizal fungi (AMF) on the water use effect of alfalfa was revealed. At the same time, the mechanism of AMF's water transport and impact on soil hydraulic characteristics was explored. Finally, through field experiments, the effects of reconstructed soil layer and AMF inoculation on soil water retention and plant efficient water use were verified, providing feasible ideas for ecological reconstruction in mining areas. The main research findings are as follows:

(1)In order to explore the suitable reconstructed soil layers for coal mine waste disposal sites, it was found that the one-dimensional vertical movement of the wetting peak increased with the prolongation of infiltration time through the study of the soil evapotranspiration characteristics of five reconstructed soil layers and their effects on plant growth. The infiltration characteristics of reconstructed layered soil are good, the total evaporation is small, the soil evaporation capacity is low, and the evaporation inhibition rate is high. The aboveground and underground biomass of plants in reconstructed layered soil is higher than that in homogeneous sandy soil. Especially, the reconstructed layered soil of loess with a depth of 20 - 40 cm below the surface has the highest aboveground and underground biomass of plants, as well as the highest root length density, root volume, and root surface area at different soil depths. Additionally, the length of fine roots (diameter <1 mm) is also the longest. Therefore, the reconstructed layered soil with loess at a depth of 20 - 40 cm below the surface has better evapotranspiration characteristics and is more conducive to plant growth, making it a suitable choice for reconstructing soil layers in the western arid and semi-arid coal mining area.

(2)In order to reveal the effect of AMF on the water use efficiency of alfalfa, the distribution patterns of soil moisture and plant roots at different depths were studied by reconstructing soil layers and inoculating AMF. The results show that the soil moisture content in the 20 - 40 cm loess layer of the reconstructed layered soil is very high (> 30%), and the moisture content in the 40 - 100 cm soil layer is also relatively high (20 - 25%). In different soil depths, the root biomass of reconstructed layered soil is higher than that of homogeneous soil. The root density of AMF inoculation was higher than that of non inoculation treatment. In different soil depths, the root biomass of AMF inoculation was significantly higher than that of non inoculation treatment, especially in the 0 - 20 cm soil layer. Compared with non inoculation, AMF inoculation reduced the water absorption ratio of alfalfa in the shallow layer by 12.00% and 14.10% in the reconstructed layered soil treatment and homogeneous soil treatment, respectively. Reconstructing layered soil and inoculating with AMF resulted in a decrease in the proportion of water absorption by alfalfa in shallow soil, while an increase in the proportion of water absorption by middle and deep soil. In arid and semi-arid areas, it can lead to higher ecological plasticity of plants. Meanwhile, inoculation with AMF increases plant leaves δ¹³C promotes plant water use efficiency.

(3)In order to investigate the mechanism of water transport from AMF to alfalfa under drought conditions, the water transport process of AMF to the host alfalfa was directly tracked and quantified using heavy oxygen water (labeled as ¹⁸O) in different soil substrates (high moisture treatment, 70% of field water capacity; low moisture treatment, 40% of field water capacity). It was found that regardless of whether the soil matrix was under high or low moisture treatment, AMF significantly enriched ¹⁸O in the roots, stems, leaves, and transpiration water of alfalfa that absorbed heavy oxygen water, indicating that AMF can directly absorb water. In high moisture soil matrix, the amount of water transferred by AMF to alfalfa is 0.26 ± 0.02 mL·d^-1, accounting for 12.32 ± 1.06% of the total transpiration water of alfalfa. In low moisture soil matrix, the amount of water transferred by AMF to alfalfa is 0.12 ± 0.02 mL·d^-1, accounting for 17.03 ± 1.59% of the total transpiration water of alfalfa. Compared to plant transpiration requirements, the direct water transport from AMF to alfalfa cannot be ignored, and the contribution of AMF to water transport to alfalfa is more important in low moisture soil matrices than in high moisture soil matrices.

(4) In order to investigate the impact mechanism of AMF on soil hydraulic characteristics, the effects of water conditions (low water treatment, 40% of field capacity; high water treatment, 70% of field capacity) and levels of AMF inoculation (with and without AMF inoculation) on soil hydraulic characteristics (water retention and hydraulic conductivity) were studied. It was found that the saturated hydraulic conductivity of soil treated with AMF decreased by 16.84% and 29.03% in low and high moisture soil matrices, respectively, compared to the non inoculation treatment. The soil capillary porosity of AMF treated soil increased by 5.04% and 10.38% in low and high moisture soil matrices, respectively, compared to the non AMF treated soil. The change in non capillary porosity is exactly opposite to capillary porosity. The soil moisture characteristic curve of AMF treatment was higher in both low and high moisture soil matrices than the corresponding non inoculation treatment, indicating that AMF inoculation can change the soil moisture characteristic curve and increase soil water holding capacity. High moisture soil matrix affects soil hydraulic characteristics by affecting colonization rate, colonization intensity, and hyphal density in AMF treatment.

(5)In order to verify the effects of reconstructing soil layers and inoculating AMF on soil moisture retention and improving plant water use strategies, field experiments were conducted to study the effects of reconstructing soil layers and inoculating AMF on efficient water use for plants. It was found that compared with homogeneous soil, the plant height in reconstructed layered soil increased by 7.13% and 29.11%, respectively, in treatments without and with AMF inoculation; The SPAD values of plants increased by 2.42% and 35.19%, respectively. Reconstructing the layered soil profile resulted in a significant increase in soil moisture, total nitrogen, total phosphorus, and total potassium content at 20-40 cm. Compared with homogeneous soil, reconstructed layered soil can increase the total biomass of plant roots. The content of total nitrogen, total phosphorus, and total potassium in the soil treated with AMF inoculation was significantly lower than that of the non inoculation treatment at different depths, indicating that AMF inoculation increased the utilization of soil nutrients by alfalfa. Compared with the non inoculation treatment, the AMF inoculation treatment increased the total biomass of plant roots by 2.8 times and 2.3 times respectively in homogeneous soil and reconstructed layered soil treatment, and the total fine root length density by 2 times and 1.6 times, respectively. The MixSIAR model was used to analyze the absorption ratio of alfalfa to soil moisture at different depths in different treatments. Reconstructing layered soil and inoculating AMF can effectively change plant water use strategies, reduce the water absorption ratio of plants to the 0 - 20 cm soil layer, and increase the water absorption ratio to the 20 - 40 cm and 40 - 100 cm soil layers. The combined treatment of reconstructing layered soil profiles and inoculating AM fungi has a more significant improvement effect on plant water use strategies, transforming the main water source of alfalfa into 20 - 40 cm. This is beneficial for plants in arid and semi-arid coal mining areas in the western region to utilize deeper soil moisture, reducing their dependence on 0-20 cm soil layer moisture.