黄河源区不同退化程度高寒草原群落生产力、物种多样性和土壤特性及其关系研究

近些年来，气候暖干化和过度放牧导致黄河源区高寒草原发生明显退化，严重影响了当地畜牧业和环境的可持续发展。退化后，植被群落生产力、物种多样性和土壤因子之间相互作用、相互影响，使生态系统持续恶化。以往的研究中研究人员对退化后群落生产力和物种多样性关系关注较多，但对退化过程中土壤要素变化的重视程度往往不够。因此，探究不同退化程度下高寒草原群落生产力、物种多样性和土壤特性及其关系对于认识高寒草地退化过程及退化草地恢复具有重要现实意义。在黄河源区采用空间分布代替时间演替的方法，根据植被和土壤特征选取了未退化到严重退化5个退化梯度，探讨不同退化程度下高寒草原群落生产力、物种多样性和土壤特性及其关系。结果表明：1）随着退化程度的加剧，群落地上和地下生物量均呈先稳定后降低的趋势，在轻度退化阶段达到最大值，重度和严重退化阶段显著降低；2）Shannon-Wiener多样性指数在轻度和中度退化阶段显著增加了20%和15%（P=0.025和P=0.039），均匀度指数从未退化到重度退化变化不明显，严重退化阶段物种多样性指数均显著降低；3）土壤水分、各深度土壤有机碳、全氮、铵态氮和硝态氮均呈先稳定后降低的变化规律，土壤容重随着退化程度的加剧而显著增加；4）群落生物量、物种多样性与土壤养分呈正相关关系，与土壤容重呈负相关关系，冗余分析结果显示土壤容重、硝态氮、有机碳是退化过程中驱动植被因子变化的主要因素。因此，针对不同退化阶段采取不同的恢复治理措施，尤其是改善土壤养分和物理性质，同时对中度和重度退化两个关键阶段应该给予更多的关注。

Plant productivity, species diversity, soil properties, and their relationships in an alpine steppe under different degradation degrees at the source of the Yellow River

In recent years, overgrazing and an increasingly warm and dry climate have resulted in significant degradation of the alpine grasslands in the source region of the Yellow River, which has seriously harmed both the sustainable development of local animal husbandry and the environment. After degradation, the interaction between vegetation productivity, species diversity, and soil nutrients can aggravate the degradation of alpine grasslands. Most previous studies have focused on community productivity, species diversity, and their relationships after degradation; however, the change in soil elements in the process of degradation is often neglected. Exploring the relationship between vegetation community productivity, species diversity, and soil nutrients has important practical significance to understand the degradation process of alpine grasslands and their restoration. In this study, the method of spatial distribution or temporal succession was used in the source region of the Yellow River. Five degraded gradients from intact to very severely degraded alpine steppes were selected based on the vegetation cover and the dominant species to explore the relationship between vegetation community productivity, species diversity, and soil nutrients. Our results showed: 1) with the aggravation of the degradation degree, the aboveground and belowground biomasses of the community showed a non-significant trend towards a decrease, reaching the maximum in the slightly degraded stage, and was significantly reduced in the severely and very severely degraded stages; 2) the Shannon-Wiener diversity index increased by 20% and 15% in the slightly and moderately degraded stage, respectively (P=0.025 and P=0.039, respectively); the evenness index showed a no-significant change from the intact to severely degraded stage, and the species diversity index decreased significantly in the very severely degraded stage; 3) soil moisture, organic carbon, total nitrogen, ammonium nitrogen, and nitrate nitrogen at first showed a trend towards non-significant change and then decreased, and soil bulk density increased significantly with the aggravation of degradation; 4) community biomass and species diversity were positively correlated to soil nutrient levels and was negatively correlated to the soil bulk density; redundancy analysis results showed that soil bulk density, nitrate nitrogen, and organic carbon were the main soil factors driving changes in vegetation factors during degradation. Therefore, different restoration and management measures should be adopted for different degradation stages, especially to improve soil nutrients and physical properties in the severely degraded and very severely degraded stages. At the same time, more attention should be paid to the two key stages of moderate and severe degradation.