| In recent years,climate change,overgrazing and rodent outbreaks have led to the fragmentation of alpine meadow vegetation to form a large number of bare patches,resulting in serious damage to grassland production and ecological functions.In order to explore the technical measures for restoration of degraded alpine meadows,this study used a combination of outdoor and indoor research methods to investigate the processes and causes of collapse of bare patches in alpine meadows and the succession pattern of different degraded patches,the key limiting factors for ecological restoration of patchy degraded alpine meadows,the response of no-tillage reseeding measures to micro-topographic changes in patchy degraded alpine meadows and the analysis on restoration of patchy degraded alpine meadows in the Source Zone of the Yellow River.The results of this study showed that:1.Healthy meadows include three components:soil particles,roots,and stones.The proportion of unit mass of each component in descending order of soil particles,roots,and stones.The proportion of unit volume of each component in descending order of roots,soil particles,and stones.There is no significant difference in soil texture composition（sand,silt,and clay）among different degraded patches.Under the effects of overgrazing,frequent disturbances as caused by plateau pikas（Ochotona curzoniae）,and freeze-thaw alternation,alpine meadows lead to vegetation fragmentation and root system decay,soil particles naturally settle to forming bare patches.2.The natural succession within plateau pikas disturbed patches and the joint effects within plateau pika and plateau zokor（Myospalax baileyi）disturbed patches significantly improved plant diversity,richness,and biomass（P<0.05）.Natural succession of bare patches promoted increased soil moisture,soil nutrients,and microbial biomass,thereby significantly increased N-acetyl-β-D-glucosaminidase（NAG）+leucine aminopeptidase（LAP）and acid phosphatase（AP）enzyme activities（P<0.05）.There were differences in soil microbial nutrient limitations during the natural succession stage of two types of rodent disturbances patches.The dominant bacteria of soil were Actinobacteria,Proteobacteria,Acidobacteriota,Ascomycota,Basidiomycota,and Mortierellomycota in the natural succession stages of the plateau pikas disturbed patches and the joint effects of plateau pika and plateau zokor disturbed patches.The natural succession stage of plateau pika disturbed patches had a highly significant positive effect on soil moisture and extracellular enzyme activity,a highly significant negative effect on soil p H（P<0.01）,and a significant positive effect of soil moisture on soil nutrients（P<0.01）.The natural succession stage of the joint effects of plateau pika and plateau zokor disturbed patches had a highly significant positive effect on soil microbial biomass,a highly significant negative effect on soil extracellular enzyme activity（P<0.01）,and a highly significant positive effect of soil moisture and microbial biomass on soil nutrients（P<0.01）.3.Soil suppression treatments of bare patches in indoor pots significantly increased plant aboveground biomass（P<0.05）.Soil moisture,water storage,bulk density,conductivity,soil compaction,cohesion and root-soil composite shear strength increased significantly with increasing compaction intensity（P<0.05）.Soil moisture was a key limiting factor affecting the ecological restoration of different degraded patches as formed by plateau pika disturbance.Bare patches significantly increased soil water storage through suppression（P<0.05）.4.Plant diversity,biomass,and soil water content increased significantly from high topography（H）to low topography（L）in no-tillage reseeding restored areas of patchy degraded alpine meadows（P<0.05）.There was a significant negative correlation between soil moisture and elevation height（P<0.05）.Soil microorganisms of different micro-topography（high topography（H）,above the average topography（AA）,below the average topography（BA）and low topography（L））were limited by the amount of N.Proteobacteria,Actinobacteria,Acidobacteriota,Ascomycota,Basidiomycota,and Mortierellomycota were the most dominant taxons in different micro-topography.The reduced elevation directly increased soil moisture,with a path coefficient of-0.89.Soil moisture has a significant positive effect on plant diversity and biomass（P<0.05）,while biomass was significantly negatively correlated with terrain height（P<0.05）.5.The application of organic fertilizer（F）,no-tillage reseeding（R）,and organic fertilizer+no-tillage reseeding（FR）show some promoting effect on soil nutrient content,microbial biomass,and extracellular enzyme activity both on sunny and shady slopes.In terms of soil microbial nutrient limitation,soil microorganisms under different remediation measures were almost all co-limited by the amount of N and P of sunny slope in 2020,soil microorganisms under different remediation measures were all limited by the amount of N and P of shady slope in 2020,sunny slope and shady slope in 2021 and 2022.Acidobacteriota,Firmicutes,Actinobacteria,Ascomycota,Mortierellomycota,Basidiomycota,and Chytridiomycota were the most dominant taxons both on sunny and shady slope in 2021 and 2022.The optimal combination restoration measure for different degraded patches in the sunny slope are 225 g·m-2organic fertilizer+1.5 g·m-2 Elymus breviaristatus cv.Tongde+0.75 g·m-2 Festuca sinensis cv.Qinghai+0.75 g·m-2 Poa crymophila cv.Qinghai,the different degraded patches in the shady slope are 75 g·m-2 organic fertilizer+1.5 g·m-2 Elymus breviaristatus cv.Tongde+0.75 g·m-2 Festuca sinensis cv.Qinghai+0.75 g·m-2 Poa crymophila cv.Qinghai. |
