甘南州不同退化程度高寒草甸植被及土壤特性的演化规律

为明确甘南州退化高寒草甸植被及土壤特性的演化规律，本研究以甘南藏族自治州碌曲县、夏河县和合作市不同退化程度高寒草甸为研究对象，调查其植被特征并采集土壤样品，测定土壤理化性质、酶活性及微生物数量。结果表明，随退化程度加深，莎草科、蔷薇科和毛茛科等科属毒杂草逐渐代替禾本科优质牧草优势位，植被高度、盖度、草产量、多样性指数降低，重度退化草地较轻度退化草地草产量降低了约2000 kg/hm²；土壤理化性质全氮、全磷、全钾、孔隙度、粉粒含量下降，pH值、全盐、容重及黏粒含量升高，由轻度至重度退化草地土壤全磷含量下降了0.67 g/kg，土壤全钾含量下降0.62 g/kg；土壤脲酶活性、蔗糖酶活性、碱性磷酸酶活性降低，蔗糖酶活性由轻度至重度退化草地降幅最大，可达0.45 mg/g/24h；土壤细菌和放线菌数量降低，真菌数量增加，重度退化草地较轻度而言细菌数量降低约5×10⁶ cfu/g，放线菌降低约5×10⁵ cfu/g，真菌增加约2×10³ cfu/g；相关性分析发现各因子与退化程度的相关性性强，相关系数在0.92以上，多为0.99甚至1。因此，甘南州高寒草甸随退化程度加深，总体呈现出草地优势种消失，植被高度、盖度、草产量、多样性下降，土壤养分及活性降低，并呈现向盐碱化、荒漠化演替的趋势。本研究为甘南州高寒草甸生态系统退化预测、管理、恢复等方案的制定提供理论依据。

Evolution regularity of degraded alpine meadow vegetation and soil characteristics at different degrees in Gannan Tibetan Autonomous Prefecture

The alpine meadow on Qinghai Tibet Plateau is an important component of alpine meadow ecosystem and grassland agroecosystem in the world, in which Gannan Prefecture alpine meadow plays a critical role in biodiversity conservation, ecosystems sustainable development, regulating the global climate and the carbon cycle process. But the degradation trend of it now is becoming severer and severer, 18.08% of its total grassland acreage is in danger and continuous deteriorate. As a result, retrograde succession occurs and brings about a serious threat to the world ecological security, while there are few studies about the evolution process, especially in the synthesis of multi-ecological factors, and few refer to the managing role of microbiome. Furthermore, amount researches showed the complexes of vegetation, soil and microorganism is critical to study the evolution regular of the degraded alpine meadow. Therefore, there were 3 aspects for the investigation and analysis according to the principle, and all samples were collected from the alpine meadow with different degradation degrees, light, moderate and severe degrees, in Luqu County, Xiahe County and Hezuo City respectively. The vegetation characteristics were analyzed, and the soil samples were collected for determining soil physiochemical properties, enzyme activity and microbial quantity. The result showed that with the deepening of degradation, the vegetation height, coverage, grass yield, and diversity indexes decreased, while the poisonous weeds such as Cyperaceae, Rosaceae and Ranunculaceae gradually replaced the dominant position of high-quality forages of Gramineae, and the grass yield of severely degraded grassland decreased almost 2000 kg/hm² by comparing with the lightly degraded grassland, which signify the alpine meadow weakening feasibility for grazing. The physicochemical properties of soil changed greatly, the dominant components of soil nutrients and soil enzymes served for the circulation of matter and flow of energy in the system, as well as the particles related to the sub-composition of soil structure changed in different ways. The soil total phosphorus, total potassium, porosity and silt generally decreased, while soil pH value, total salt, bulk density and clay showed an opposite direction. The soil total phosphorus and total potassium content decreased by 0.67 g/kg, 0.62 g/kg, respectively, when the degradation degree from light to severe. For the soil enzyme activities, soil urease activity, sucrase activity, alkaline phosphatase activity dropped, the decrease of sucrase activity from light to severe degradation degree was the largest, up to 0.45 mg/g/24h. The changing ways of soil physiochemical properties, enzyme activity could be concluded that the soil degradation was becoming more and more serious. Soil microorganisms were the most diverse community in the biosphere and the transition of their existence state was an indispensable driving force of biogeochemical cycle. The number of bacteria in soil microbial composition was the largest but its amount dropped significantly. The actinomycetes were also with the same trend along the degradation process, however, the number of fungi increased continuously. The number of bacteria, actinomycetes and fungi decreased by 5×10⁶ cfu/g, 5×10⁵ cfu/g and 2×10³ cfu/g, respectively, with the degradation trend from light to severe degree. Correlation analysis showed that each factor had a strong correlation with the degradation degree, and the correlation coefficient was above 0.92, most of which were 0.99 or even 1. Generally, with the deepening of degradation, the dominant grassland species disappeared, vegetation height, coverage, grass yield and diversity decreased, soil nutrients and activity decreased, and showed a trend of salinization and desertification. This study provides a theoretical support for the formulation of the prediction, management and restoration schemes of the alpine meadow ecosystem degradation in Gannan.