【作者】 刘芳；

【导师】 杨劼；

【作者基本信息】 内蒙古大学 ， 生态学， 2011， 博士

【摘要】 茭蒿(Artemisia giraldii)隶属菊科(Composiate)蒿属(Artemisia),多年生草本状半灌木,以茭蒿为建群种的干草原是我国温带南部和暖温带森林草原带及典型草原带南部边缘地区的重要草原类型,同时茭蒿也是重要的水土保持植物。茭蒿能够特异分布于黄土丘陵沟壑区的沟谷中,且长期、稳定的存在。沟壑交错的地貌导致热量、水分等环境因子在沟谷中重新分配,使得沟谷成为一种不同于地带性生境的特殊生境。选取位于鄂尔多斯高原东北部、黄土高原北缘的丘陵沟壑区作为研究区,从个体、种群、群落三个层面入手研究茭蒿对沟谷特殊生境的适应性,以期揭示茭蒿的生态适应机制,为黄土丘陵沟壑区植被建植和水土保持综合治理提供科学依据。主要研究结果如下：1、茭蒿的区系地理分布茭蒿的地理分布范围为E101°-116°,N34°-41°,海拔390-2800m之间,其现代分布中心为黄土高原,茭蒿现代分布中心的形成是在茭蒿不断适应黄土地质和黄土高原环境变化中协同进化而来的。2、茭蒿群落及生境特征(1)、茭蒿适合分布于黄土丘陵沟壑区30°-50°的陡沟坡上,坡度小于或大于这一范围,茭蒿的生物量均明显下降,表明30°-50°左右的黄土沟坡为茭蒿特异占领的生境。(2)、茭蒿在黄土沟谷中形成以它为建群种的群落类型,其中在沟谷阳坡形成茭蒿单优群落,群落盖度低,物种种类贫乏,平均生物量为13.88g·m-2；在沟谷阴坡与硬质早熟禾形成共建群落,群落盖度较高,物种种类较丰富,平均生物量较高,为36.55g·m-2。(3)、茭蒿群落生境相比梁顶生境具有以下特征：土壤容重小、孔隙度大、易被侵蚀；土壤TOC、全氮、速效氮含量低,土壤贫瘠；水分散失较快。3、茭蒿种群特征(1)、茭蒿种群年龄结构在沟谷阴坡为增长型,在阳坡为稳定型；相比梁顶,茭蒿在沟谷中具有高的种群密度和根冠比。(2)、茭蒿种群在梁顶生境中随着撂荒恢复演替的进行,分布格局由随机分布转向小尺度聚集分布再转变为较大尺度聚集分布,与此同时,种群空斑面积显著增加,种群领地减小；而在沟谷生境中茭蒿种群呈现典型的随机分布,种群空斑面积显著低于梁面各群落,种群领地显著高于梁顶。(3)、梁顶—沟谷的生境梯度上,茭蒿的生态位宽度最大,表明其具有较强的资源利用能力,对环境的适应能力较强,可以广泛分布在梁顶和沟谷各种生境中；与茭蒿生态位重叠程度较高的一组植物中大多数是梁顶植物群落演替前期优势程度较高或出现较早的物种,表明从生态位属性上看茭蒿为一个演替前期物种。4、茭蒿繁殖特征(1)、茭蒿种群的生殖分配以无性繁殖为主,仅投入很少的一部分能量用于有性繁殖。(2)、茭蒿种子质量很小,千粒重仅为0.0901±0.0051g,这种特性有利于其种子的传播；茭蒿种子质量虽然很小,但在相同条件下,与其他植物种子发芽率并没有表现出显著差异,即种子质量的大小没有对茭蒿种子的萌发造成影响。(3)、沟谷中茭蒿每基株分生的无性系分株数量最多,无性繁殖的平均扩散面积最大；梁顶上的茭蒿基株具有最少的无性系分株数和最小的平均扩散面积。表明沟谷生境中茭蒿的无性繁殖能力优于梁顶生境。(4)、土壤种子库中,75%的茭蒿种子位于0-5cm土层中；沟谷中茭蒿种子表现出随着沟谷稳定程度的增加,种子密度增大,并且始终都是群落土壤种子库中重要值最大的物种；梁顶上的土壤种子库中,茭蒿的种子密度是所有生境中最低的,重要值显著下降。表明,沟谷中的茭蒿种群具有较强的繁殖潜力。5、茭蒿的生理生化特征从叶片的水分生理特征上看,茭蒿与本氏针茅和铁杆蒿的抗旱性没有显著差别；生理生化指标分析表明,茭蒿与本氏针茅和铁杆蒿表现出的抗旱性接近,不同生境中的茭蒿种群所表现出的抗旱性也接近,均无显著差异。表明茭蒿具有一定的抗旱性,能够适应沟谷中较为干旱的生境特征。6、茭蒿的生态效应茭蒿在黄土丘陵较陡沟坡上可以长期、稳定存在并形成优势度较高的群落,作为一种天然分布于此的群落类型,茭蒿群落具有自组织、自维持的特性。因此,茭蒿是黄土丘陵沟壑区陡坡水土流失治理的优良物种。更多还原

【Abstract】 Artemisia giraldii is an herbaceous subshrub of Compositae family. It constitutes steppe plant communities found in the forest-steppe subzone and the typical steppe subzone of the southern part of the warm temperate zone in China. The species plays an important role in soil and water conservation in this area. The plant is very common in Loess Plateau and has colonized its loess hill and gully region. This specific habitat is formed by a network of numerous gullies and hilly ridges. Such landform heterogeneity, characterized by high fragmentation, is responsible for redistribution of water and heat resources. We chose this loess hill and gully region, situated in the north-east of Ordos Plateau and north of Loess Plateau, as the study area. Systematic analyses of Artemisia giraldii at individual, population, and community levels were conducted to elucidate its ecological adaptability to the gully habitat and develop strategies for maintaining vegetation structure and sound soil and water conservation practices in this region. Main results of the study are as follows:1. Geographical distribution of Artemisia giraldiiArtemisia giraldii is generally found in the area between 101°and 116°of eastern longitude and 34°and 41°of northern latitude at the elevation range of 390-2800 m. The main areal of the species is centered on Loess Plateau indicating evolutionary adaptation of Artemisia giraldii to environmental character of this area.2. Community structure and habitat characteristics of Artemisia giraldii(1) We found that the optimal topographic slope for Artemisia giraldii growth was about 30°-50°. Biomass of Artemisia giraldii was substantially lower at localities above or below this value. This finding suggests that Artemisia giraldii has adapted to this gully habitat.(2) Artemisia giraldii formed two major plant communities on slopes of loess gullies. The monodominant community of sunlit slopes has lower coverage, lower species richness, and smaller average biomass of 13.88 g·m-2. Shaded slopes are occupied by a community co-dominated with Poa sphondylodes. It is characterized by higher coverage, higher species richness, and larger average biomass (36.55 g·m-2).(3) Soil properties of slopes occupied by Artemisia giraldii are quite different from soils covering ridge tops. They are characterized by smaller soil bulk density and higher soil porosity, which means they are easily eroded. Soil water under Artemisia giraldii communities is diffused faster. Slope soils are also poorer as shown by lower contents of total organic carbon (TOC), total nitrogen, and readily available nitrogen.3. Population structure of Artemisia giraldii(1) Demographic structure of Artemisia giraldii populations correlates with slope conditions. Shaded slopes have higher abundance of older individuals compared with sunlit slopes. Population densities and root-to-top ratios of Artemisia giraldii growing in gullies were higher than those on hills and ridge tops.(2) As a result of restorative succession processes after field abandonment on the ridge top, the spatial pattern of Artemisia giraldii changed from initially random to clumped at finer scale and, later, clumped at large scale. These changes were accompanied by significant overall population increase and the simultaneous decrease of the habitat area. Spatial patterns of the plant are typically random in gullies, and the area occupied by its populations is significantly smaller when compared to the ridge top. At the same time, the area occupied by Artemisia giraldii is larger than that of the ridge top.(3) Artemisia giraldii has the widest ecological niche which allowed it to utilized resources available and adapt equally well along the habitat gradient from hill ridge top to a gully. Our findings suggest that Artemisia giraldii has significant niche overlap with other species that were dominant in these communities at the earlier stages of succession and appeared earlier in the succession series. We conclude that Artemisia giraldii was a dominant species at the beginning of succession.4. Reproduction ecology of Artemisia giraldii(1) Data on reproductive allocation of Artemisia giraldii revealed that most of energy expenses of the plant were channeled to asexual reproduction and only a little was used for sexual production. (2) The weight of 1000 seeds of Artemisia giraldii was 0.0901±0.0051 g. We hypothesize this trait allows the species to achieve higher dispersal rate. Seed germination rate of Artemisia giraldii was not different from other species with similar traits. This suggests that smaller seed weight of Artemisia giraldii was not an advantage for the success of seed germination.(3) The number of ramets per genet and the asexual reproduction average diffusion area per genet of Artemisia giraldii were highest in the gully and smallest in the ridge tops.(4) Soil seed bank data showed that 75% of Artemisia giraldii seeds were concentrated in the soil at the depth of 0-5 cm. As the gully stabilizes, the seed density in the soil seed bank of Artemisia giraldii increases and its value of importance is the highest in all communities. The seed density was lowest at the ridge top and its value of importance decreased significantly.5. Physiological characteristics of Artemisia giraldiiWe compared water physical characteristics of Artemisia giraldii, Artemisia sacrorum and Stipa bungeana, and found no significant differences in their drought resistance traits. Analyses of physiological characteristics of these three species also revealed their similarity in term of drought resistance. Our findings suggest that Artemisia giraldii has developed drought resistance and adapted to dry conditions in the gully habitat.6. The overall ecological effect of Artemisia giraldiiArtemisia giraldii grows on the 40°slopes of loess gullies. It can persist there a long time and forms communities in which it plays a dominant role. Being a natural vegetation, Artemisia giraldii-formed communities self-organize and perform quite well in the area. We therefore consider it as a species useful for soil and water conservation in the hilly-gully region更多还原