【作者】 周杰；

【导师】 郭正刚； 韩天虎；

【作者基本信息】 兰州大学 ， 农业推广（专业学位）， 2013， 硕士

【摘要】 高寒草甸是青藏高原草地生态系统中的主体植被类型,不仅孕育着丰富的乡土生物资源,蕴藏着珍贵的高山植物抗逆基因,支撑着高原草地特色畜牧业,而且调蓄着江河水源,维系区域生态安全。然而高寒草甸的退化严重威胁着流域生态、区域生产和生计的安全。高寒草甸退化的致因主要有人为因素和自然因素,人为因素的研究主要集中于放牧和工程建设,自然因素的研究主要集中于全球变暖和鼠害。虽然冻融是高寒草甸退化的重要因素,但目前关于冻融导致高寒草甸退化的研究相对零星。本研究在青藏高原北部多年冻土区,基于冻融退化程度,选择了未退化、轻度、中度和重度退化四个阶段的样区,通过调查不同样区草地植物群落组成、总盖度、高度、多样性、地上生物量、分析优势种植物和土壤的碳氮磷含量,阐明青藏高原多年冻土区高寒草甸冻融退化过程中草地植物群落变化的特征,明晰不同退化阶段优势种植物和土壤的生态化学计量特征,从植物群落组分改良和养分限制的角度提出了退化高寒草甸的恢复策略。得到以下主要结果：1明晰了高寒草甸冻融退化过程中群落组分的变化特征高寒草甸植物群落组分伴随着冻融退化发生明显变化,表现为随着冻融退化程度加剧,莎草科和禾本科植物优势种地位逐渐削弱,而豆科和菊科的毒杂草组分却逐渐增加。2查清了高寒草甸群落特征和生产力对冻融退化的响应高寒草甸冻融退化过程中植物群落盖度和样方内丰富度先升后降,高度和地上生物量逐渐降低,而β多样性指数却升高,说明生境异质化增加。3揭示了冻融退化对草甸优势种碳氮磷化学计量特征的影响高寒草甸冻融退化过程中优势植物青藏苔草的C含量没有明显变化,N和P含量逐渐减小,而C：N、N：P和C：P比值却逐渐增加。轻度退化和未退化草地,优势种N：P介于14-16之间,其生长受NP共同限制,中度和重度退化阶段,优势种生长受P限制,需增施磷肥。4明确了土壤碳氮磷化学计量特征对冻融退化的响应高寒草甸冻融退化过程中土壤C、N和P含量逐渐降低,N：P和C：P也均逐渐减小,说明土壤养分逐渐流失,需要增施土壤养分,保证土壤养分的供给量。5提出了退化高寒草甸恢复的策略通过点播方式,补充扁蓿豆和垂穗披碱草,以及青海早熟禾；通过其他能源替代家畜粪便,将牛羊粪回归天然草甸,通过添施鸡粪,鸭粪和鸽粪,改善优势植物生长受P限制的现状。更多还原

【Abstract】 Alpine meadow is the main vegetation type of grassland ecosystem in the Qinghai-Tibet Plateau, and it has rich native biological resources and precious alpine plant with anti-stresses genes, plays important roles in animal production with plateau characteristics, regulates river catchment capacity and maintains regional ecological security. However, the degeneration of alpine meadow seriously threatens ecological, productive and livelihood security throughout the rivers. The factors contributing to alpine meadow degradation mainly include artificial and natural factors, in which grazing and engineering construction are mainly artificial factors and global warming and rat trouble are mainly natural factors, neglecting freezing-thawing cycle, which is an important factor to cause alpine meadow degradation. On the basis of different degree of freezing-thawing degradation, This study investigated the composition of plant communities, cover, height, diversity and aboveground biomass and determined the content of C, N and P in dominant plants and soil at natural, light, moderate and severe degradation stages of alpine meadow caused freezing-thawing cycle for clarifying the features of alpine meadow and stoichiometry in the process of freezing-thawing cycle, which would benefit to propose the recovery strategies for the alpine meadow degradation from optimizing plant community composition and improving nutrient supply in the permafrost region of the northern Tibetan Plateau. The main results were as following,1. The features of plant communities at natural, light, moderate and severe degradation stages was clarified in this studyThis study showed that the plant community composition of alpine meadow at natural, light, moderate and severe degradation stages was different, indicating that the domination of sedge and gramineous plants gradually decreased, and poisonous and unpalatable plants in leguminosae and compositae gradually increased as the freezing-thawing degradation increased.2. This study explained the response of community and productivity of alpine meadow to freezing-thawing degradationPlant community cover and species richness index firstly increased and then decreased, and community height and aboveground biomass decreased gradually, while (3-diversity index increased in the process of freezing-thawing degradation, indicating that the freezing-thawing degradation increased the habitat heterogeneity in the study region.3. This study disclosed the effect of the freezing-thawing degradation on C, N, P stoichiometry of dominant plants of alpine meadowThe results of this study showed that the freezing-thawing degradation did not affect the C content and decreased the N and P content of Carex moorcroftii, while C:N, N:P and C:P of Carex moorcroftii increased gradually, probably caused by a greater shortage of soil P in the study areas, which suggested that the application of phosphate fertilizer is beneficial to encourage the healthy growth of dominant species.4. This study explained the respose of C, N, P stoichiometry of alpine meadow soil to freezing-thawing degradationThe C, N, P content and N:P and C:P in soil decreased with the increase of freezing-thawing degradation, indicating that the soil nutrient lost gradually in the process of freezing-thawing cycle, which suggested that the supply of soil nutrient is a basic way to restore alpine meadow degradation.5. This study proposed the restorable strategies for alpine meadow degradationThis study proposed that the Medicago ruthenica from legumes and Elymus nutans and Qinghai bluegrass from gramineous were used to sow by mixture though bunch and reseeding pattern. The cattle and sheep manure had to return to natural meadow by finding other energy instead of animal feces. and poultry dung was used to improve the situation P limitation.更多还原