【作者】 梁向锋；

【导师】 赵世伟；

【作者基本信息】 中国科学院研究生院（教育部水土保持与生态环境研究中心） ， 土壤学， 2008， 硕士

【摘要】 子午岭林区是黄土高原保存最完整的天然次生林区。该区北部目前还保存有空间上完整的植被正向演替系列,即弃耕地先锋群落→草本群落(白羊草Bothriochloaischemum、茭蒿Artenmisia giradii +长芒草Stipa bungeana、铁杆蒿Artenmisia sacrorum、大油芒Spodiopogen sibiricus +苦参Sophora flavecens、黄菅草Themeda japonica或野古草Arundinella anomala)→灌丛群落(沙棘Hippophae rhamnoides、狼牙刺Sophora viciifdia、虎榛子Ostryopsis davidiam)→早期森林群落(乔灌群聚、山杨Populus davidiana、白桦Betula platyphylla、侧柏Platycladus orientalis、油松Pinus tabulaeformis)→辽东栎群落(Quercus liaotungensis)。山杨(Populus davidiana)、白桦(Betula platyphylla)和侧柏(Platycladus orientalis)为演替的过程时期,气候的演替顶级为辽东栎林(Quercus liaotungensis)。通过分析各个群落(弃耕地、先锋草地、草本群落(白羊草)、灌丛群落(沙棘、狼牙刺)、早期森林群落(山杨、白桦、山辽混交)、辽东栎群落0-100 cm内土壤容重、结构、水分常数、入渗性能、水分环境的变化规律及相互关系,初步探讨了植被正向演替过程中土壤物理特征变化的趋势和影响土壤水分环境变化的机理。主要结论如下: (1)植被恢复改善了土壤结构和孔隙状况。植被恢复降低了土壤0-5 cm、5-10 cm、10-30 cm土层的土壤容重。植被恢复到灌丛以后,其表层容重均小于1.0 g/cm3,山杨、辽东栎降低土壤容重的作用最为明显。土壤孔隙度的变化主要表现在通气孔隙度的增加和总孔隙度的增加,无效孔隙和毛管孔隙变化不大。按照由弃耕地、沙棘、白羊草、山杨到辽东栎的植被演替顺序,土壤孔隙分形维数在整个土壤剖面上都有所提高;而土壤水稳性团聚体分形维数依次降低。各个植被群落均能明显改善土壤结构,增强土壤结构的稳定性。而团聚体平均重量直径不能反映土壤结构在0-100 cm土层和植被恢复过程中的这种变化规律。土壤水稳性团聚体分维、孔隙分维均能作为评价土壤结构稳定性的指标;而团聚体平均重量直径仅可作为大团聚体含量的指标。土壤水稳性团聚体分维、孔隙分维比团聚体平均重量直径更适合作为描述植被恢复下土壤结构稳定性变化的指标。(2)植被恢复过程中土壤水分常数的变化植被演替过程中土壤持水力为:辽东栎>山杨>狼牙刺>白羊草>沙棘。除沙棘外,各植被土壤持水力和供水力随植被的正向演替而提高。土壤比水容量即释水能力表现为乔木林大于灌木林和草地。土壤有机碳含量与土壤持水性能有很好的相关性,相关系数达到0.8左右。提高土壤有机碳含量可以改善土壤的持水性能。(3)植被恢复提高了土壤的饱和导水率植被恢复有利于提高土壤0-60 cm土层的饱和导水率,土壤饱和导水率随着土层深度的增加而降低;随着植被恢复而提高。饱和导水率在剖面上的平均值以辽东栎顶级群落最高1.918 mm/min。土壤的容重、毛管孔隙度、>0.25 mm水稳性团聚体含量及粘粒含量直接影响土壤饱和导水率。有机质含量达到51.56 g/kg以前,饱和导水率随着有机质含量的提高而提高,可以认为是土壤饱和导水率提高的驱动因子;在高于51.56 g/kg时,土壤有机质含量的提高反而会降低土壤饱和导水率。这在黄土高原是极其少见的,需要进一步深入研究。(4)植被恢复过程中土壤水分环境的变化植被生长期间,植物群落的耗水趋势一致。相同气候条件下,0-5 m土层土壤储水量早期森林、草地最高,灌丛最低。土壤储水量恢复的差异主要表现在,辽东栎群落3 m以下土层土壤储水量高于灌丛群落,特别是4-5 m土层,不仅高于灌丛群落,而且已接近其他群落水平。说明子午岭次生辽东栎群落深层土壤储水量开始并已经得到恢复。土壤储水量在垂直方向上的变异,草地最小,并在2 m或3 m以下的土层达到相对稳定。早期森林、辽东栎3-4 m和4-5 m的变异仍未稳定,说明其植被耗水影响到了5 m以下土层。早期森林、辽东栎在降雨充足的年份,能够较其它群落使得更多水分入渗,这与其良好的土壤结构和高饱和导水率有关。植被恢复主要是降低了了0-30 cm土层的土壤容重,提高了0-30 cm总孔隙度、通气孔隙度,提高了0-60 cm土层的土壤饱和导水率,改善了土壤0-30 cm的结构,随着植被的不断恢复,向着高入渗率和好的保水性能方向发展。实际上植被恢复到灌丛阶段后,其结构就已经有了飞跃式的变化,之后随着恢复年限的增加变化速度减慢,早期森林阶段进一步变好,顶级群落时,形成与气候、植被相适应的“顶级土壤状态”。具有一定的保水、蓄水功能。更多还原

【Abstract】 Ziwuling region has developed with various vegetations of secondary forest in Loess Plateau. In different phases of development, vegetation systems in this region have changed from pioneer herbage species initially recovering in abandoned cropping lands (Bothriochloaischemum, Artenmisia giradii + Stipa bungeana, Artenmisia sacrorum, Spodiopogen sibiricus +Sophora flavecens, Themeda japonica or Arundinella anomala) to secondary shrubs (Hippophae rhamnoides, Sophora viciifdia, Ostryopsis davidiam), early forest community (Populus davidiana, Betula platyphylla, Platycladus orientalis, Pinus tabulaeformis), and finally Quercus liaotungensis community as the climax forest. In this study, soil profiles (0-5 cm、5-10 cm、10-30 cm、30-60 cm、60-100 cm soil layers ) were selected from typical vegetation systems representing for vegetation successions in the region. From the analysis of the change of soil bulk density, soil structure, soil water constant, soil saturated hydraulic conductivity and soil water environment under different vegetations in soil profiles. The tendency of soil physical character change and the mechanism of soil water environment change in the course of vegetation succession were discussed. The main results are as follows:(1) Soil structure and porosity condition were improved in the course of vegetation successionVegetation restoration reduced soil bulk density in 0-5 cm, 5-10 cm and 10-30 cm layers. In the stage of shrub, soil bulk density was less than 1.0 g/cm3. Soil bulk density was significantly lessed in Populus davidiana and Quercus liaotungensis. Soil total porosity and macropore were increased significantly,but capillary pore has no big change.Soil aggregate fractal dimension, pore fractal dimension and the aggregate MWD ( mean weight diameter ) can reflect soil structure stability in different approaches. The aggregate fractal dimension and soil pore fractal dimension are both extremely correlative to the content of >0.25 mm aggregate, the content of soil organic carbon and soil bulk density. So they can be used as the indexes to evaluate soil structure stability. MWD has no significant correlation with the content of soil organic carbon,soil bulk density. There is a positive correlation between MWD and the content of >5 mm soil water atable aggregate. It only can be used as the index to evaluate the content of big soil aggregate. Compared with abandon farmland, the soil structure was improved under the other four vegetations.(2) The change of soil moisture constant in the course of vegetation restoration Among the five communities the soil water holding capacity had the following order: Quercus liaotungensis > Populus davidiana> Sophora viciifolia> Bothriochloa ischaemum> Seabuckthorn. Soil water holding capacity improved with vegetation succession except for Seabuckthorn.The specific water capacity(water release capacity)shown as forest> shrub, grassland. The parameter A, the soil available water and unavailable water all had a good correlation to the content of soil organic carbon (g / kg), and the correlation coefficient up to 0.83, 0.80 and 0.79 respectively.(3) Saturated Hydraulic Conductivity was increased in the course of vegetation restorationValues of soil saturated hydraulic conductivity quickly reduced with depth under different communities. Values of soil saturated hydraulic conductivity were significantly improved in 0-60 cm layer in the course of vegetation restoration. The average soil saturated hydraulic conductivity for each soil layer progressively declined from that for Quercus liaotungensis to early forest, to shrub, to Pioneer grassland and to farmland abandoned to Bothriochloa ischaemum, respectively. Quercus liaotungensis supported the highest values under the nine stands, with vegetative restoration notability improving Ks. Soil saturated hydraulic conductivity was directly affected by soil bulk density, capillary porosity, > 0.25 mm aggregate content and clay content. Soil physical properties such as soil bulk density, capillary porosity and aggregate content were all improved by soil organic matter content.Before the soil organic matter content up to 51.56 g/kg, it is the driving facter of soil saturated hydraulic conductivity. But after the soil organic matter content up to 51.56 g/kg, the value of soil saturated hydraulic conductivity would be decreased with SOM increasing. This is extremely rare in the Loess Plateau, its need further study.(4) Soil moisture environment changes in the course of vegetation restorationThe different communities had the same trend of water consuomption. Either in different year or month, soil water storage under shrub is all the lowest, early forest and grassland are the highest. Deep soil water storage under early forest is higher than Quercus liaotungensis, which favorable for its succession to Quercus liaotungensis. Soil water storage under Quercus liaotungensis is higher than shrub when the depth larger than 3 m, 4-5m. Deep soil water was recovered.Soil bulk density in 0-30 cm layer is decreased, and total porosity in 0-30 cm layer is increased, soil saturated hydraulic conductivity in 0-60 cm layer was raised, soil structure in 0-30 cm layer was improved with vegetation restoration. With the vegetation recovery, soil became more and more high infiltration rate and water holding capacity. In fact, vegetation restoration to shrub stage, its structure has been a leap of change. The rate of change slow-down with the restoration year increased, Soil was further improved under early forest. When the vegetation restored to Quercus liaotungensis community, the soil became the climax soil which adapt to the vegetation and the climate. The climax soil has some water holding features.更多还原