黄土高原退耕植被根系分布特征与环境响应

【作者】 李艳；

【导师】 赵忠；

【作者基本信息】 西北农林科技大学 ， 林学， 2007， 硕士

【摘要】 论文针对我国西部地区生态环境建设中的主要内容,以黄土高原植被自然恢复过程中不同演替阶段的植被群落为研究对象,通过调查取样,分析不同演替阶段植被根系特征,揭示根系生物量及长度等形态指标的时空变化规律,阐明不同演替阶段植被根系动态特征与土壤资源利用模式及其与环境之间的响应关系,揭示退耕生态系统发展变化的地下根系行为机制,为我国西部地区植被建设与生态环境修复提供理论和技术支撑。通过系统分析研究,主要取得了以下成果:1.植被恢复初期,植被根系生物量在深层土壤中的相对分布量较多,随着植被演替的不断进行,植被类型从一年生植被类型向多年生植被类型演替,相应的植被根系的分布特征也逐渐发生变化,表层土壤中根系的相对含量逐渐增加。在天然草地上,大部分植被根系主要集中表层0-40cm土壤中2.从根系消失系数的分布特征可以看出,一年生植被根系垂直分布特征参数β的数值较大,说明在这一阶段,植被根系在深层土壤中的分布比例较大;而多年生植被根系垂直分布特征参数β的数值较小,说明在这一阶段,植被根系大多集中在土壤表层,深层土壤中分配的比例较小3.在草地植被演替阶段,土壤水稳性团聚体的含量具有不同的特征。总的来说,随着土壤深度的增加,>0.25mm水稳性团聚体的含量逐渐降低,说明植被根系对于土壤的作用逐渐降低。所有各个径级的土壤团聚体中,只有直径在1-2mm范围内的土壤团聚体表现出了随着土壤深度增加而减少的趋势,其分布特征与植被根系的分布特征相似。说明该径级范围内的土壤团聚体具有较好的指示性。随着植被恢复时间的延长,较大径级的水稳性团聚体含量逐渐增加,在土壤中垂直分布的规律性也逐渐增强。4.退耕初期,草地土壤有机质的含量相对较低;而在退耕超过20年和天然草地上,土壤有机质的状况有了明显的改善:表层土壤的有机质含量有了明显的增加,深层土壤的有机质含量也有了一定程度的提高。5.对土地退化/恢复过程中土壤水稳性团聚体及有机质的动态变化规律的研究结果表明:林地开垦后土壤中各级水稳性团聚体含量均呈下降趋势,且大粒径团聚体下降趋势较大;土地退化过程中,土壤中>0.25mm水稳性团聚体含量减少;土地恢复过程中,土壤中>0.25mm水稳性团聚体含量增加;土壤有机质含量随着开垦/恢复年限的增加而减少或增加,且在开垦/恢复的前期,有机质含量变化迅速;土壤有机质含量与>0.25mm土壤水稳性团聚体含量之间存在着显著的正相关关系:y = 23.195x + 12.12;土壤水稳性团聚体平均重量粒径随着土壤中>0.25mm水稳性团聚体含量或退耕年限的增加而增加。6.通过对不同植被恢复年限小区的土壤特性的取样分析及根系调查分析结果表明:植被根系的存在,改善和提高了土壤的物理化学性质,增加了土壤有机质及水稳性团粒的含量,在此基础上建立了植被根系生物量与土壤性质之间的定量关系。更多还原

【Abstract】 Referring to the main content in ecological construction in West China, systematic researches were carried out to study the root distribution characters of vegetation at different succession stages. Dynamic characters of main root index (including root biomass, root length, root surface area, and root volume, etc) of vegetation at different succession stages were revealed. And corresponding relation between root index and soil factors was setup, which helped to reveal the root behavior mechanics for ecosystem development, and provided scientific and technological support to vegetation construction and ecological restoration in loess region. Based on the above analysis, following researches can be reached:1. During the rehabilitating succession process, root biomass of vegetation on returned farmlands changed with the rehabilitating time. At the initial stages, more roots were distributed in the deeper soil. With the development of vegetation succession, vegetation type changed from annual types to perennial types, more roots were concentrated in the upper soil. To the vegetation on natural grassland, its root system was concentrated in surface 0~40cm soil layer. All the other root indexes, including root length, root surface area etc, showed similar distribution patterns.2. Analysis of root extinction coefficient showed that this parameter decreased with the increase of abandoned years, which indicated that there was more root concentrated in the surface soil layer with the increase of abandoned time. This kind root distribution pattern on abandoned lands improved soil physical and chemical characters, and favored the intrusion of new species and vegetation succession.3. Soil aggregate content was different at different succession stages. Generally, soil aggregate with its diameter larger than 0.25mm decreased with the increase of soil depth, which indicated the decrease of root influence on soil aggregate. Among the soil aggregate of all diameter classes, only the aggregate with its diameter between 1 mm and 2 mm showed similar trends with root biomass, which implied its better indication with root. With the increase of restoration years, aggregate increased with larger diameter, and in vertical direction. also increased.4. At the initial time of restoration, soil organic matter content was relative low, with the development of vegetation succession, soil organic matter increased. When the restoration time was over 20 yrs, soil organic matter content was higher, which was similar to what was on natural grassland. And the soil organic matter content in deeper soil increased with larger diameter, too.5. Researches on dynamics of water stable aggregate in land degradation and restoration process indicated that after reclamation, water stable aggregate decreased and bigger size particle tended to decrease much, >0.25mm soil water stable aggregate increased during the restoration years, soil organic content decreased or increased with the land degradation or restoration and during the former years, they changed rapidly, there existed positive linear relation between soil organic content and water stable aggregate (Φ>0.25 mm): y = 23.195x + 12.12, mean weight particle size of soil water stable aggregate increased corresponding with the content of >0.25mm soil water stable aggregate or restoration years. Land restoration augments the mean weight particle size of soil water stable aggregate through the increase of soil water stable aggregate content and its stability was enhanced, soil structure was improved.6. Analysis of soil characters and root distribution characters on lands with different restoration years indicated that, both soil physical and chemical properties were ameliorated due to the existence of root biomass, and soil organic matter content and aggregate content were increased too. Quantitative relation between root biomass and soil factors was set up based on the above analysis.更多还原