【作者】 周旗；

【导师】 赵景波；

【作者基本信息】 陕西师范大学 ， 自然地理学， 2005， 博士

【摘要】 针对黄土高原存在的土壤干层现象和部分人对黄土高原生态环境建设成果产生怀疑的问题,本文以黄土高原自然环境相对较好的关中平原为研究区,应用野外钻孔采样测量土壤含水量和理论分析等方法,对土壤干层的判定标准、土壤干层的形成机制、黄土高原土壤干层的分布范围、土壤干层的恢复条件、关中东西部土壤干层发育强度的时空差异以及该区以何种植被地带类型为标准进行植被建设等一系列问题进行了系统研究,以期能对黄土高原未来的植被建设提供科学支持。 通过研究,获得的主要进展和新认识包括: ① 创造性地从土壤水分供给和植物水分需求两个方面确定了土壤干层的判定标准。依据对植物生长的限制程度将土壤干层划分为土壤干化层和土壤干旱层两种类型,确定了土壤干层的湿度标准。土壤干化层(The dried soil layer)的湿度范围在土壤稳定湿度和土壤初始凋萎湿度之间,主要表现为土壤对植物的供水发生困难。土壤干旱层(The soil drougllt layer)的湿度范围是低于土壤初始凋萎湿度。表明植物已经受到干旱胁迫,出现凋萎现象甚至死亡。 ② 对咸阳、兴平地区土壤水分进行了实验研究,结果显示该区在枯水年和平水年中龄及以上的人工林下有明显的土壤干层发育,这说明人工林下土壤干层的分布范围已经扩展到黄土高原南部地区,而不是过去认为的只分布在关中以北地区。进一步对宝鸡金台区、咸阳武功县和渭南临渭区的采样测量显示,在关中平原,土壤干层的发育程度从西向东有逐渐增强的趋势,成片非经济林下的土壤水分明显低于单株树,也低于经济林。而在丰水年,关中平原的土壤干层已基本消失,显示该区在年降水量大于800mm的丰水年,土壤干层能够恢复。 ③ 提出了土壤剖面水分分布格局取决于渗透重力水的入渗深度、临界蒸发/蒸腾深度和地下水埋深三者在剖面上组合关系。根据化学元素的淀积深度理论,初步判定关中平原的渗透重力水的入渗深度一般在200cm左右,个别情况达到350～400cm。通过分析大气蒸发和植物根系的分布,初步断定关中平原大气蒸发的深度在200cm左右,最大可达400cm,而人工林的耗水深度可以超出500cm,但强烈耗水深度一般在400cm以上。 ④ 明确地提出了土壤薄膜水带的存在是土壤干层形成的必要条件,而人工林强更多还原

【Abstract】 Aimed at the phenomenon of dried soil layer existing in loess plateau and the doubt to the results of vegetation construction by someone, a series of questions such as the determinant criterion, the formation mechanism, the distribution, the renew condition of the soil dried layer in loess plateau, the time-space diversity of the soil dried layer forming in difference area of Guanzhong Plain, and the goals of vegetation construction, had been discussed based on the data of soil moisture content obtained from the samples which sampled by the light manpower drill and measured by electronic balance. The main achievements and new cognition are as follow:1. The determinant criterion of soil-dried layers has been proposed firstly from two aspects of soil water supply and vegetation water demand, and the soil-dried layer has been taken into two difference types according to its restricting extent to vegetation growth. One is the dried soil layer, which range of soil moisture content is from soil stabilization humidity to soil elementary languish humidity, and indicate the difficulty to meet demand of soil water in vegetation growth. Another is the soil drought layer, which range of soil moisture content is from soil elementary languish humidity to 0 theoretically. We named weak soil drought layer that range of soil moisture content is between the elementary languish humidity and stabilization languish humidity which indicate the vegetation growth had been stress by lack of soil water, and appeared languish but can growth, and named the strong soil drought layer that range of soil moisture content is below the stabilization languish humidity which indicate the vegetation growth had been stress strongly by lack of soil water, and appeared languish, withered and died.2. The data, which obtained from measure of soil moisture content in Xianyang and Xingping area, indicate that there are soil-dried layer developing obviously under the manmade forest in middle ages and older, and illuminated that the phenomenon of soil -dried layer has spread to the southern loess plateau, Guanzhong plain, which nature conditions are the best in loess plateau, in the low water years and the average years. More study on Baoji city, Wugong country and Weinan city showed that the growthdegree of soil-dried layer has an enhanced trend gradually from western to eastern in Guanzhong Plain. The disappeared of soil-dried layer in abundant water year in Guanzgong plain indicate that the renew of soil-dried layer under the condition of more than 800mm in annual precipitation has been realized.3. Deduced and Confirmed the infiltration depth of gravity-capillary water at a loess profiles in Guanzhong plain is 200cm or so in usually, 300-350cm in the extreme, by use of the theory of depth in chemical composition transfer and the experimentation of infiltration depth of gravity-capillary water. Concluded that violence evaporation depth of air is 200cm or so in usually, 400cm in the extreme, and the water consumed depth of vegetation growth is more than 500cm, but its violence used depth is 400cm or so, by analysis the air evaporation and pattern of root system distribution.4. The condition of forming the soil dry layer has been proposed definitely that exist of the membrane water hosepipe is the necessary condition and the bury depth of vegetation and gas spending soil water is deeper than depth of gravity-capillary water infiltration, which are the sufficient condition for forming the soil dry layer. In loess plateau district, the moisture content in the membrane water hosepipe is lowness, and its transfer speed is very slow. Those make the membrane water hosepipe become the direct moisture factor of the development of the soil dry layer in this area. The facts we discovered that water retrieved in the membrane water hosepipe is very slowly once it’s consumed. The thickness of the membrane water hosepipe and the gravity-capillary hosepipe is complementation. In the same soil profile, the thicker the gravity-capillary hosepipe, the thinner the membrane water hosepipe.5. The bio-climatic mechanism of soil dried layer forming has been proposed. The decrease of precipitation, which conduced shoaling the infiltration depth of gravity capillary water, and made deeper the depth of evaporation of soil and vegetation at the same time, results in climatic drought. On the other hand, the adaptation to climatic drought of vegetation is to develop the vegetation of perpendicularity spread root system pattern and to restrict the level spread pattern, which made deeper on the depth of soil water consume by vegetation. Integrated three factors above, the soil-dried layer must be formed once the depth of water use is deeper than the infiltration depth of gravity-capillary water, and the forming degree of soil-dried layer is stronger with the development of drought. So, the exist of soil-dried layer is respond of soil moisture更多还原