【作者】 王晓春；

【导师】 龙瑞军； 尚占环；

【作者基本信息】 兰州大学 ， 生态学， 2022， 硕士

【摘要】 草地退化从多方面影响着草地生态功能。高寒生态系统土壤细菌、真菌和病毒结构和功能越来越受到重视,那么与其他土壤微生物组分相比,土壤病毒在草地退化过程中究竟如何变化?并如何影响草地生态功能?这个问题是深入理解高寒草地退化过程中地下生态机制的一个关键,也是进一步掌握在未来气候变化与人类活动背景下,高寒地区土壤病毒生态安全风险的认知过程,更是高寒草地生态系统健康评价与管理的重要科学依据。基于此目的,该研究以青藏高原祁连山高寒退化草地为研究对象,采用数量分类和排序方法,通过对调查高寒草地28个大样地140个样方的5个植被指标、7个土壤指标进行数量分类与排序分析,确定了4个不同退化程度等级。进一步对4个不同退化程度的28个样地,采用宏病毒组测定土壤病毒,高通量测序法测定土壤细菌和真菌序列。分析了草地退化过程中土壤细菌、真菌和土壤病毒变化规律和功能,并通过相关性分析、零模型、冗余分析、结构方程模型等方法,研究植被、土壤理化性质、土壤微生物及草地生态功能之间的关系。主要结果如下:(1)祁连山不同退化程度的高寒草地中植被和土壤特征各不相同。未退化、轻度退化、中度退化、重度退化的草地植被覆盖度范围为80～100%、51～88%、49～69%、27～47%。土壤有机碳含量的范围为145.95～148.49 g/kg、35.15～85.73g/kg、29.54～57.82 g/kg、11.36～19.60 g/kg。(2)土壤细菌和真菌的多样性和物种组成在草地退化过程中发生了改变。在中度退化草地中,细菌和真菌物种多样性最高。处于未退化和重度退化的草地中细菌和真菌物种组成差异显著(P<0.05)。在未退化的草地中,变形菌门(Proteobacteria)和脱硫菌门(Desulfobacterota)显著高于其他退化程度的草地。绿弯菌门(Chloroflexi)在重度退化的草地中显著高于其他退化程度的草地。子囊菌门(Ascomycota)和担子菌门(Basidiomycota)在未退化草地中显著高于其他退化程度的草地。土壤p H和土壤有机碳是影响细菌和真菌群落结构的主要因素。(3)草地退化影响了土壤微生物组装过程。在细菌和真菌组装过程中,随机性过程和确定性过程都发挥了作用,但以扩散限制为主的随机性过程占据主导地位。在重度退化草地中,细菌和真菌随机性过程贡献率最高,分别为90.96%和82.54%。(4)病毒基因功能预测结果表明高寒退化草地中存在与氨基酸代谢和碳水化合物代谢等功能相关的代谢基因,其中大部分辅助碳水化合物代谢基因参与复杂多糖的降解从而促进退化草地碳循环。(5)草地退化影响生态多功能性。结构方程模型表明,草地退化造成土壤p H增加,土壤病毒α多样性降低,导致草地生态多功能性的降低,草地退化过程中,土壤病毒侵染细菌菌群,降低草地生态多功能性,退化草地土壤病毒对高寒草地健康存在一定的生态安全风险。综上,祁连山地区高寒草地退化通过影响病毒物种多样性影响细菌物种多样性进而影响真菌物种多样性,并对草地生态功能造成影响。在草地退化过程中,细菌、真菌的物种多样性均在中度退化草地中达到最高,而病毒在未退化草地中物种多样性最高,中度退化草地中次之。此外,该研究发现土壤病毒降低细菌多样性,影响草地生态功能。因此在草地管理中,使用微生物和病毒结合分析能够增加对草地生态健康认识的准确度,有助于更加科学的进行草地管理。更多还原

【Abstract】 Grassland degradation affects the grassland ecological function in many aspects.More attention is being paid to the structure and function of soil bacteria,fungi,and virus in alpine ecosystems.Then compared with other soil microbial components,how do soil viruses change during grassland degradation? And how to affect the grassland ecological function.This problem is a key to deeply understand the underground ecological mechanism in the process of alpine grassland degradation.It is also to further grasp the cognition of the ecological security risk of soil viruses in alpine areas under the background of future climate change and human activities.And it is also an important scientific basis for the health evaluation and management of alpine grassland ecosystem.For this purpose,in the Qilian Mountains grassland on the Qinghai-Tibet Plateau,adopted quantitative classification and sorting methods to analyze 5 vegetation indicators and 7 soil indexes in 140 plots of 28 large large plots of alpine gegraded grassland,and determine 4 different degradation grades by quantitative ecological method.Further for 28 plots with 4 different degrees of degradation,soil viruses were determined by virome and soil bacterial and fungal sequences were determined by the high-throughput sequencing.The change laws and functions of soil bacteria,fungi and soil viruses in the process of grassland degradation are analyzed,and the relationship between vegetation,soil physical and chemical properties,soil microorganisms and grassland ecological functions is studied through correlation analysis,null model,redundancy analysis and structural equation model.The main results are as follows:(1)Vegetation and soil characteristics vary in alpine grasslands with different degrees of degradation.The vegetation coverage of non-degraded grassland,lightly degraded grassland,moderately degraded grassland and severely degraded grassland ranged from 80 ～ 100%,51 ～ 88%,49% ～ 69% and 27 ～ 47%.The organic carbon content of the soil ranged from 145.95 ～ 148.49 g/kg,35.15 ～ 85.73 g/kg,29.54 ～ 57.82g/kg and 11.36 ～ 19.60 g/kg.(2)Bacterial and fungal diversity and species composition change during grassland degradation.Bacterial and fungal species diversity was highest in moderately degraded grasslands.The composition of bacterial and fungal species varied significantly between non-degraded grassland and severely degraded grassland(P <0.05).In non-degraded grasslands,Proteobacteria and Desulfobacterota were significantly higher in non-degraded grasslands than in other degraded grasslands.Chloroflexi is significantly higher in severely degraded grassland than other degraded grasslands.Ascomycota and Basidiomycota were significantly higher in non-degraded than other degraded grasslands.Soil p H and soil organic carbon are the main factors influencing bacterial and fungal community structure.(3)Grassland degradation affects the soil microbial assembly process.Both stochastic processes and deterministic processes function in both bacterial and fungal assembly,but stochastic processes dominated by dispersal limitation predominate.In the severely degraded grassland,bacterial and fungi stochastic processes contributed highest rate,were 90.96% and 82.54%,respectively.(4)The viral gene function prediction result indicates that metabolic genes with functions related to amino acid metabolism and carbohydrate metabolism exist in alpine degraded grassland,most of which are auxiliary carbohydrate metabolism genes are involved in the degradation of complex polysaccharides to promote the carbon cycle in degraded grassland.(5)Grassland degradation affects the ecological multifunctionality.Structural equation model shows that grassland degradation leads to the increase of soil p H,the decrease of soil virus α diversity,and the decrease of grassland ecological multifunctionality.In the process of grassland degradation,soil viruses infect bacterial flora and reduce grassland ecological multifunctionality,and degraded grassland soil viruses have certain ecological security risks to the health of alpine grassland.It is concluded that the degradation of alpine grassland in the Qilian Mountains affects the diversity of bacterial and then the fungal diversity,and affects the ecological function of the grassland.During grassland degradation,the diversity of bacteria and fungi reached the highest in moderately degraded grassland,while the virus was the highest in non-degraded grassland,and second in moderately degraded grassland.Moreover,the study found that soil viruses reduce bacterial α diversity and affect grassland ecological function.So,in the future grassland management,we can use the microbial and viral diversity and community structure to predict the health status of the land,and to effectively manage the degraded grasslands.更多还原