【作者】 刘永俊；

【导师】 冯虎元；

【作者基本信息】 兰州大学 ， 植物学， 2012， 博士

【摘要】 丛枝菌根(arbuscular mycorrhiza, AM)真菌是一类非常重要的植物共生微生物,能与大部分陆生植物根系形成互惠共生体,是地上地下生态系统相互联系的重要节点,影响着生态系统的整个过程。AM真菌不仅是生态系统功能的敏感指示剂,而且它们的物种及功能多样性是维持农业和生态环境可持续发展的关键所在。人类活动如何影响AM真菌的群落结构及其功能,是生态学家关注的热点问题之一。青藏高原和黄土高原是特殊的生态系统,生态环境极其脆弱,该地区AM真菌研究非常薄弱,有些地方近乎空白,难以对该地区的生态系统管理和生态恢复提供理论指导和技术支撑。本文在青藏高原和黄土高原地区研究了几种人类扰动生态系统的AM真菌多样性及群落结构,阐明了地膜覆盖、植被破坏及施肥对AM真菌的影响规律。主要研究结果如下：(1)、在黄土高原半干旱区的春小麦样地中,地膜覆盖显著提高了AM侵染率和孢子密度；小麦根中共发现9个AM真菌分子种,但地膜覆盖处理对AM真菌的物种丰富度无显著影响(小麦根中的平均AM真菌丰富度,覆膜：5±0.7,未覆膜：4.6±0.5)；地膜覆盖会特异性激活或抑制某些种类的AM真菌,进而造成AM真菌群落结构的显著变化；地膜覆盖导致的AM真菌变化主要由土壤速效磷、含水量等土壤性质的变化所引起。(2)、在青藏公路沿线的高海拔地区(海拔4,500-4,800m),从历史植被破坏斑块中生长的异叶青兰(Dracocephalum heterophyllum;先锋物种)和未破坏原生群落中生长的多枝黄耆(Astragalus polycladus;演替晚期物种)根际共检测出21个AM真菌分子种,包括8个新种和1个新科。异叶青兰(5.4±0.49)根系中AM真菌的平均物种丰富度要显著高于多枝黄耆(1.93±0.25)；此外,多枝黄耆根系中无丛枝结构(营养交换结构),但异叶青兰根系的丛枝侵染率高达12.8%;上述结果表明该地区的先锋物种比演替晚期物种更偏好与AM真菌形成互惠共生体。植被覆盖度是影响该区域AM真菌群落组成的重要因子,植被退化严重的区域,AM真菌的物种丰富度较低。(3)、在青藏高原高寒草甸生态系统的长期氮磷施肥样地中(海拔3,500m),共检测出38个AM真菌分子种；随施肥浓度上升,植物群落平均物种丰富度从27.6下降至4.4,植物根系内平均AM真菌分子种丰富度从13下降至4.6,AM侵染率从41.2%下降至12.7%,根际土壤的AM真菌菌丝生物量也下降了约3倍；高浓度氮磷施肥对AM真菌有明显的抑制作用,导致AM真菌物种多样性及功能丧失;在群落水平上,长期氮磷施肥对植物根系内AM真菌群落的影响主要由植物群落结构的变化所引起。(4)、长期的进化和相互适应使得AM真菌与植物和土壤环境之间形成了一种稳定的互作关系,植物及土壤环境对AM真菌具有重要的影响；人类扰动如施肥、植被破坏、农艺措施等均会改变AM真菌的群落结构及物种多样性,进而影响生态系统的稳定性和可持续性。更多还原

【Abstract】 Arbuscular mycorrhizal (AM) fungi can form mutualistic associations with the roots of most terrestrial plants. It is well established that the AM fungi play key roles in linking the aboveground and belowground ecosystems, and consequently, influence many terrestrial ecosystem processes. In addition, AM fungi can serve as an indicator of the ecosystem functioning, and the importances of AM fungal species and functional diversity are well appreciated in maintaining the sustainability of ecosystems. In recent decades, many ecologists have focused on the species compositions and functions of AM fungal communities in natural conditions, especially those anthropogenic disturbed ecosystems. Nonetheless, less is known about the AM fungal communities in the Loess Plateau and Qinghai-Tibet Plateau of China, where the ecosystems are unique and fragile, so that it is difficult to us to direct the sustainable management and restoration of disturbed ecoystems in this region. In this dissertation, I chose several anthropogenic disturbed ecosystems to investigate the effects of plastic film mulch, vegetation damage and fertilization on the species diversities and community compositions of AM fungi. The main results of this dissertation are listed below.(1) In the dry-land spring wheat field of Loess Plateau, AM colonization and spore density were increased significantly by the plastic film mulch (PFM). A total of nine AM fungal phylotypes was detected in wheat roots under PFM and no-PFM treatments, whereas the phylotype richness of AM fungi were similar between treatments (PFM:5±0.7; no-PFM:4.6±0.5). The PFM treatment could specifically activate or inhibit some AM fungal taxa to colonize wheat roots, resulting in distinct shifts of AM fungal community compositions. Changes of AM fungal variables under the PFM treatment were mainly attributed to the changes in soil properties such as available phosphorus and soil moisture.(2) In the regions with very high altitude (4,500-4,800m a.s.l.) along the Qinghai-Tibetan highway, a total of21AM fungal phylotypes were detected from the rhizospheres (based on roots and spores) of Dracocephalum heterophyllum (pioneer species) in sites disturbed30years ago and Astragalus polycladus (late-successional species) in undisturbed vegetation, including eight new AM fungal species and one new family-like clade. More AM fungal phylotypes colonized root samples of D. heterophyllum (5.4±0.49) than of A. polycladus (1.93±0.25); moreover, no arbuscules (nutrient exchange structure) were observed in the roots of A. polycladus, whereas the arbuscular colonization of D. heterophyllum was12.8%. These findings suggest that AM fungi would prefer to colonize pioneer species rather than late-successional species in this region. We also found that the vegetation coverage was an important factor in regulating AM fungal community, with a low AM fungal diversity detected in regions with serious vegetation degradation.(3) A total of38AM fungal phylotypes was identified from a long-term nitrogen and phosphorus fertilization site (3,500m a.s.1.) in the alpine meadow ecosystem of Qinghai-Tibet Plateau. With the increasing levels of fertilization, the plant species richness, phylotype richness of AM fungi in roots and AM colonization reduced from27.6to4.4, from13to4.4and from41.2%to12.7%, respectively. The highest level of fertilization caused the extraradical AM fungal hyphal biomass to decline by three-fold. High fertilizer inputs had strong negative effects on AM fungi, rusulting in dramatical loss of biodiversity and functions of AM fungal community. At the community-scale, response of AM fungal communities colonizing roots to long-term fertilization was strongly linked to the shifts of plant communities due to fertilization, suggesting the plant community composition is a key determinant in influencing the AM fungal assemblage.(4) The relationships among AM fungi, plants and soil environment are stabilied by long-term co-evolution and co-adaptation in a local scale, and consequently, any changes of plant and soil components will generate greatly effects on AM fungi. Anthropogenic disturbances such as fertilization, vegetation damage and agronomic practices will affect negatively the diversity and composition of AM fungal community, and influence the sustainability of ecosystems.更多还原