【作者】 解迎革；

【导师】 王国栋；

【作者基本信息】 西北农林科技大学 ， 土壤学， 2012， 博士

【摘要】 近几十年来，受全球气候变化的影响，部分地区的植物生长出现衰退甚至死亡现象。为了研究植物生长对全球气候变化的响应，需要对土壤—根系系统内的水分状况有一定的了解。土壤贮水能力是指土壤所保持的可供植物利用的水分储量，决定了在干旱期内有多少水分可以供植物吸收利用，在季节性干旱条件下土壤贮水能力是植物生长的重要限制因子。多石质林地土壤内部砾石含量、土层厚度等具有较强空间变异性，现有的研究手段在应用于多石质林地土壤时难以以点代面，在应用时也具有较大难度。对多石质林地土壤的特性及变化无法进行全面和立体的反映，使得对林地石质土壤的贮水性能认识受到一定限制。本文采用电阻率断层扫描技术，可立体的反映石质土壤内部空间的特性，对多石质林地土壤的电阻率特性和持水性能进行研究，对影响贮水能力的因素及其影响程度进行了分析，并对该技术应用于土壤电阻率特性与树木生长之间的关系进行了探索性研究。得到以下主要结论：(1)采用四电极法对细土样品的电阻率进行，测定结果表明含水量是引起细土样品电阻率值变化的主要原因。表层土壤由于具有较高的有机质含量而表现出特殊的电阻率特性。压力膜仪对砾石与细土的持水特性研究表明，相比于细土部分，所研究地区砾石对土壤持水性能的贡献可以被忽略。(2)通过将石质土壤看做由砾石镶嵌于细土中而组成的二相介质，采用二维电阻率断层扫描技术，数值模拟了不同砾石体积含量的石质土壤。结果表明对已知二相各自电阻率特征值的石质土壤，其等效电阻率与其中砾石体积含量相关，数值模拟结果与理论预测结果相符合。验证了电阻率断层扫描技术应用土壤中砾石体积含量估计的可适用性，提出在土壤较湿润时为该技术的适宜使用条件。(3)土壤砾石体积含量的野外实际测定结果对估计结果进行了验证，实测值和有效电阻率之间的关系与理论预测结果相吻合，且细土电阻率值对二者之间关系影响较大。若设定细土电阻率为单一的优化值160m，对砾石体积含量估计的绝对误差为22%。(4)研究地区基岩的特征电阻率值为1200~1600m，采用电阻率断层扫描技术对影响石质土壤贮水能力的另一重要特性—土层厚度进行了有效研究，确定了基岩位置及其变化范围。明确了对林地石质土壤进行贮水能力评估的土壤传递函数并对各参数进行确定。(5)土壤中砾石体积含量和土壤厚度及细土的持水能力被用于对土壤的贮水能力进行评估。相比于砾石体积含量误差所引起的对土壤贮水能力评估的影响，来自于土层厚度的影响程度较小。(6)多石质林地土壤电阻率特性与树木生长状况存在显著对应关系。三维电阻率断层扫描技术的应用，更为精确和详细的对树木立地土壤电阻率特性进行反映。(7)树木生长指标和立地土壤电阻率定量研究表明，树木的生长指标与土壤电阻率存在相关性。大型树木应对外界环境、气候变化表现出更强的适应性。在研究区域的立地土壤条件下，根系和土壤之间的作用导致根际区电阻率值较高，树木立地土壤内部不同水平切面的电阻率和树木的生长指标关系之间表现出一定的相关性。本文的相关实验和探测表明，电阻率断层扫描技术对于基于石质土壤的相关研究具有良好的可适用性，具有省力和高效等特点。所得到理论分析和实验结果，有助于提高人们对林地石质土壤的认识，将为林地石质土壤相关问题的研究提供重要指导。电阻率断层扫描技术也将会成为土壤学基础研究的一个重要工具，对其应用的进一步研究将会对土壤学相关研究提供重要的帮助。更多还原

【Abstract】 During the last decades, tree growth declining was found in some areas of the world forthe reason of the climate change. For analyzing the response of tree growth to the globalclimate change, it is necessary to get some information for the moisture status of the soil-rootsystem. Water storage capacity (WSC) which defined as the amount of water stored in soilthat is available for the vegetation, it is an important limiting factor for the tree growth inseasonal drought area. However, most of the foresty soil stands on rocky areas which showsstrong spatial varation, it is diffcult to get an overview of the inner information withtraditional methods. Electrical resistivity tomography (ERT) was applied to stony forest soilsand helped to have an overall grasp of the soil spatial varation. In our research, electricalproperties and the WSC of the stony forest soils were studied through ERT. We analyzed theinfluencing factors of the WSC and their influcing degree was analyzed as well, in addition,the applicability of the ERT for studying the relationship between the electrical resistivity (ER)of soil and the tree growth was evaluated. Some important conclusions were drawn asfollows:(1) Electrical resistivity measurements on fine earth samples with four-electrode methodindicated that the moisture content acted as the main driver in ER variation. The electricalresistivity of samples from the upper layers (0~20cm) is much higher than that in the deeperlayers, which is likely due to the high organic matter content acting as highly resistivecomponent. The water holding capability of fine earth and rock fragments was measured bypressure-plate apparatus, the results indicated that the water stored in the rock fragments ishard to be extracted by the trees and the contribution to the WSC can be neglected comparedto the fine earth.(2) Numerical simulations were performed to validate the applicability of the ERT forRFC evaluation. Stony soils with different volumetric rock fragments content (RFC) werenumerically simulated by regarding the soil as biphasic media with rock fragments embeddedin fine earth continum. With known ER of the two phases, the effective ER of the soil can be related to the RFC, the relationship was well modelled by the mixing law of Bussian’s. Themixing law was verified to be efficient and the wettest condition is favored for theapplication.(3) Estimation of RFC using ERT measurements was evaluated against referencesobtained by digging pits. It shows that the ER of fine earth has a strong impact. Considering asingle electrical resistivity for fine earth as160m, we obtained an absolute error for thevolumetric rock fragment content of22%.(4) ERT was also applicated to the evaluation of another important facot affecting theWSC, i.e. soil thickness. Soil thickness was defined as the distance between soil surface andthe bedrock. A threshold value of the electrical resistivity is proposed to be within1200~1600m, it was applied to separate the bedrock and soils media. Pedo-transferfunctions and the elements related were clarified for the WSC evaluation.(5) Estimation of the rock fragments content and the soil thickness were combined withhydraulic properties of the fine earth to map the WSC. The accuracy of the evaluation wasmuch more affected by the RFC estimaton.(6) There exists significantly correlation between the ER of the tree soil stand and thetree growth status on the Transect.3-D ERT survey can be an ideal alternation which canprovide much more accurately and detailedly for the ER of tree soil stand.(7) The research on the ER of the soils stand from3-D ERT survey indicated that the treegrowth characteristics can be correlated to the ER. Big trees are more adaptable to the climatechange on the research site. Under the condition of the soil stand, root-soil interaction insidethe vadose zone causes the increase of the ER of the soil. Different magnitude of thecorrelation was found between the ER of the horizontal slices and the tree growthcharacteristics.Some theoretical analysis and experimental results indicated that the ERT is applicabilityfor object-based stony soils, which can be laborsaving and efficiently. The results can behelpful for the unstanding of the foresty stony soils, can provide an important guide for therelated foresty stony soil problem solving.2-D or3-D ERT survey will be an important toolfor the soil fundamental research, the research on the applicaton of the method will bemeaningful for the soil related research.更多还原