Abstract:

Alpine meadows, a significant type of grassland in China, play an indispensable role in ecological function and economic value. Owing to the interference of adverse conditions, such as climate change and overgrazing, alpine meadow ecosystems on the Qinghai-Tibet Plateau have experienced varying degrees of degradation. “Black soil beaches” represent an extreme form of grassland degradation, characterized by the expansion of bald spots, with vegetation coverage below 30%. The dominant plant species shift from sedge family plants to toxic and harmful miscellaneous grass plants, and the density of rodent burrows is extremely high and distributed across all alpine grasslands in the country. However, there are differences in vegetation types and soil physicochemical properties in black soil beaches across different regions, and closely related microbial communities differ in composition and structure. Microorganisms are the most sensitive biological factors that respond to environmental changes, and have attracted great attention for their community diversity and assembly processes. Fungi and bacteria are important organisms in the soil microbial community and participate in energy flow and nutrient recycling in the environment. These microorganisms are crucial for soil formation, ecosystem function, biogeochemical cycles, and pollutant decomposition. The loss of biodiversity has become a global concern, and numerous studies have shown that a reduction in microbial diversity damages ecosystem services. Changes in the composition and assembly processes of soil microbial communities may affect many ecosystem properties including aboveground plant diversity, nutrient cycling, and nutrient retention. Soil microbial communities differ in composition and assembly processes owing to differences in soil nutrient content. At the same time, the construction and succession of soil microbial communities have always been a research hotspot in microbial ecology. A complete understanding of the impact of grassland degradation on microbial construction processes is of great significance for optimizing the ecological functions of soil microorganisms. Alpine meadows at high altitudes exhibit unique environmental characteristics that affect the microbial community composition. Studies have shown that environmental factors mainly drive changes in soil microbial communities, with soil bacterial diversity and richness decreasing with increasing altitude and dominant phyla showing regional differences. For example, low-altitude areas often contain large numbers of Proteobacteria, Acidobacteria, and Bacteroidetes, whereas high-altitude areas are characterized by enrichment of Cyanobacteria, Verrucomicrobia, and Actinobacteria. Similarly, vegetation richness and diversity also change with environmental factors such as nutrients and temperature, affecting the composition and succession of related microbial communities by altering the secretions of plant roots. The differences in the microbial and soil physicochemical properties of black soil beaches in different regions remain largely unknown. Therefore, understanding the differences in microbial community construction and driving factors of community composition differences in black soil beaches across different regions is key to environmental sustainability and local land management measures, which are of great significance for the future management and restoration of black soil beaches. As a typical ecologically fragile area of the Qinghai Plateau, black soil beaches suffer from severe vegetation degradation, nutrient loss, and high spatial heterogeneity. Understanding the differences in soil microbial community characteristics of degraded grasslands in different regions of “black soil beaches” and their influencing factors can aid in the formulation of grassland restoration strategies. This study analyzed the vegetation characteristics, soil physicochemical factors, and enzyme activities of typical degraded grasslands in the Hainan Tibetan Autonomous Prefecture (YNG), Yushu Tibetan Autonomous Prefecture (BT), and Guoluo Tibetan Autonomous Prefecture (DW) of the Qinghai Province. High-throughput sequencing technology has been used to study the microbial composition, diversity, and community assembly processes in different regions. This study aimed to establish relationships between microbial communities and environmental factors, explore the assembly processes of microbial communities in black soil beaches across different regions, and identify the main factors causing differences in community composition, thereby providing new insights into the natural restoration of degraded grassland ecosystems. The results showed that: 1) compared to non-degraded grasslands, black soil beaches have significantly higher levels of pathogenic bacteria (e.g., Mortierellomycota and Planctomycetes) and significantly lower levels of symbiotic bacteria (e.g., Basidiomycota). 2) The number and diversity of fungal species in the BT region were significantly higher than those in other regions, with BT>DW>YNG, whereas differential bacterial genera in the YNG region, such as Acidobacteria and Gammaproteobacteria, showed significant negative correlations with environmental factors (except for pH value), whereas the differential bacteria in the BT and DW regions, such as Proteobacteria and Basidiobacteria, were significantly negatively correlated with environmental factors. Proteobacteria, Basidiobacteria, and others were significantly positively correlated with total phosphorus, water content, and nitrate-nitrogen (p<0.05). 3) Stochastic processes dominate the assembly of soil bacteria and fungi in the DW and BT regions, whereas deterministic processes dominate the assembly of soil bacteria and fungi in the YNG region. 4) The total potassium content and belowground biomass mainly affected the composition of soil bacterial communities in black soil beaches in the DW region, while pH was the main influencing factor for bacterial and fungal community composition in the YNG region. The bacterial communities in the BT region were mainly influenced by nitrate-nitrogen, water content, and total phosphorus. Belowground biomass, total potassium, microbial biomass phosphorus, ammonium nitrogen, total phosphorus, and vegetation diversity index were common influencing factors for fungal community composition in the BT and DW regions. There are significant differences in soil physicochemical properties across different regions of black soil beaches, which also drive changes in soil microbial community structure. Fungal diversity is more sensitive than bacterial diversity across the three regions, with significant differences, and the YNG region has the lowest microbial species and diversity. The soil fungi and bacteria in the DW and BT regions of the black soil beaches were dominated by stochastic processes, whereas those in the YNG region were dominated by deterministic processes, further confirming the uniqueness of the YNG region in terms of soil and microbial communities. Therefore, soil environmental factors affecting soil microbial community composition and structure vary across different regions and restoration strategies should be tailored according to the corresponding environmental driving factors. It is recommended that in the process of grassland restoration at the regional scale, the starting point should be to restore microbial diversity and community richness, and to adjust soil driving factors to achieve a good dynamic of microbial communities and improve soil quality.

Key words: alpine meadow, black soil beaches, degraded grassland, soil microbial community, microbial assembly, soil physicochemical properties

摘要：

黑土滩退化草地作为青海高原典型的生态脆弱地带，植被退化、养分流失严重以及空间异质性高，了解不同区域尺度下黑土滩退化草地土壤微生物群落特征差异及影响因子，有助于制定草地恢复措施策略。通过分析青海省海北（YNG）、玉树（BT）和果洛藏族自治州（DW）黑土滩退化草地植被、土壤因子和微生物群落组成及构建过程，研究不同立地条件下环境因子对微生物群落的影响。结果表明：1）较未退化草地，黑土滩土壤中的致病菌如被孢霉门（Mortierellomycota）和浮游霉菌门（Planctomycetes）含量显著增加，共生菌如担子菌门（Basidiomycota）含量显著降低；2）BT区域的真菌物种数和多样性显著高于其他区域，表现为BT>DW>YNG；3）随机性过程主导了DW和BT区域黑土滩土壤细菌和真菌的群落构建，而YNG区域黑土滩土壤细菌和真菌由确定性过程主导；4）全钾和地下生物量主要影响了DW区域黑土滩土壤细菌的群落组成，pH是YNG区域细菌和真菌群落组成的主要影响因子，而BT区域细菌群落主要受硝态氮、含水量和全磷的影响。研究表明影响不同区域黑土滩土壤微生物群落组成和结构的土壤环境因子均有差异，在恢复和调整黑土滩土壤微生物多样性时，需因地制宜，根据相应的环境驱动因子制定恢复策略。

关键词: 高寒草甸, 黑土滩, 退化草地, 土壤微生物群落, 微生物群落构建过程, 土壤理化性质