Abstract:

Ecosystem degradation poses a serious threat to the global ecological and environmental security. A complete understanding of the degradation process and its mechanisms is crucial for restoring the degraded ecosystems. Most previous studies on alpine meadow degradation lack long-term observational data, making it difficult to reasonably analyze the formation process and mechanism of degradation. This study focused on non-degraded, moderately degraded, and severely degraded alpine meadows in the Beilu River Basin of the Yangtze River source area. Based on the actual situation in the research area, the vegetation community and soil physicochemical characteristics of alpine meadows in permafrost areas, as well as their response to grassland degradation, were explored to provide a basis for understanding the degradation process and restoration of degraded alpine meadows in permafrost areas. The results showed that: 1) with the intensification of degradation in alpine meadows, both aboveground and belowground biomass significantly decreased, the dominant species of vegetation communities shifted from grasses and sedges to forbs, and deep-rooted plants increased. 2) The species richness and Shannon-Wiener diversity indices both showed a trend of first increasing and then decreasing with increasing degrees of degradation. 3) As the degree of degradation intensified, the soil bulk density, pH, and total phosphorus increased, whereas the total nitrogen, organic carbon, nitrate nitrogen, ammonium nitrogen, and available nitrogen decreased. 4) Redundancy analysis showed that the community biomass was positively correlated with soil organic carbon, total nitrogen, nitrate nitrogen, ammonium nitrogen, available nitrogen, and available phosphorus. Shannon Wiener diversity index and species richness index are negatively correlated with silt, water content, and pH, the explanatory rates of available nitrogen, available phosphorus, and soil moisture on vegetation biomass and species diversity were 57.8%, 27.3%, and 9.9%, respectively. Therefore, plant growth in degraded alpine meadows in the source area of the Yangtze River may be limited by available nutrients. In the restoration process, the restoration of soil nutrients should be considered first.

Key words: alpine meadows, grassland degradation, Qinghai-Tibet Plateau, physico-chemical characteristics, community structure, permafrost zone

摘要：

生态系统退化严重威胁着全球生态和环境安全，充分认识退化过程和机理是开展和实现退化生态系统修复的关键。以往大部分高寒草甸退化相关研究缺乏长期的观测资料，难以合理分析退化的形成过程和机理。以具有长期观测资料的长江源多年冻土区北麓河流域未退化和退化高寒草甸为对象，根据研究区实际，探讨了草地退化下植物群落结构特征和土壤理化特性的变化及其相互关系，为查明多年冻土区高寒草甸退化机理和退化草地修复提供理论依据。 结果表明：1）退化使地上和地下生物量显著降低，植物群落优势物种由浅根系的莎草科植物向深根系的杂草类植物转变；2）Shannon-Wiener多样性指数和物种丰富度指数呈单峰变化趋势，即在中度退化阶段显著增加，但在严重退化阶段显著降低；3）退化后，土壤容重、pH和总磷显著增加，但硝态氮、铵态氮、速效氮、总氮和有机碳呈降低趋势；4）冗余分析结果显示，群落生物量与土壤有机碳、总氮、硝态氮、铵态氮、速效氮和速效磷呈正相关，Shannon-Wiener多样性指数和物种丰富度指数与粉粒、水分和pH负相关，速效氮、速效磷、土壤水分对植被生物量和物种多样性的解释率分别为57.8%、27.3%和9.9%。因此，长江源多年冻土区退化高寒草甸植物生长可能主要受速效养分限制，在对其的修复过程中，应首先考虑土壤养分的恢复。

关键词: 高寒草甸, 草地退化, 青藏高原, 理化特征, 群落结构, 多年冻土区