| During the long-term uplift of the Ordos Plateau,many closed shallow dish-shaped depressions were formed,which ecologists concluded as the "three circles" model.That is to say,the beach is centered on the low depression,and the slope surrounding the beach is outward,and the outermost is the raised hard beam land.This "three circles" structure is repeated in the Ordos Plateau,forming a spatial structure of mosaic distribution.The desert steppe area crosses the central and northern parts of the Ordos Plateau from northeast to southwest.Historically,grassland desertification was caused by unreasonable human reclamation and overgrazing,since the 1990s,the implementation of ecological projects such as plantation construction,grassland replanting,and fencing has restored the vegetation coverage,diversity,and productivity of degraded grasslands,and desertification has shown a reversal trend.However,the current large-scale single plant restoration still faces sustainable restoration problems such as the decline of dominant plant populations and the depletion of soil water resources.Therefore,at a larger spatial scale,studying the annual change process of grassland soil moisture and its influencing factors including lake and wetland subsystems can provide a scientific basis for revealing the vegetation restoration and maintenance mechanism of the Ordos Plateau desert grassland and its associated systems.This study takes the complete landscape natural system including the desert wetland of the Haba Lake Nature Reserve in Yanchi County as the research object.The landscape scale includes beam land-slope land-beach land-lake,with an area of 12 km × 12 km.The construction of nature reserves promotes the natural and artificial restoration of vegetation in the study area,and some areas are even overloaded.Based on the spatial resolution of 1 km,the 12 km2 landscape unit is divided into 152 vegetation and soil survey and monitoring sample points.The specific research contents are as follows:First,based on the vegetation and soil background survey and sampling data of 152 sample points at the landscape scale in 2019,using multiple regression trees,redundancy analysis and other methods to clarify the research area after vegetation restoration and construction(including nearly 30 The natural restoration of the past 13 years and the restoration of artificial vegetation in the past 13 years),the spatial variation pattern and influencing factors of plant community types,species composition,and the influencing factors,laid the foundation for the interpretation and cognition of the annual dynamic changes of soil moisture in the study area.Secondly,around the soil moisture monitoring data of the 0-120 cm profile at the beginning and middle of each month from April to November 2020,combined with the continuous monitoring and survey data of vegetation,topography,soil texture and other biotic and abiotic factors,Kriging interpolation analysis,set pair analysis,redundancy analysis,hierarchical segmentation and other methods are used.Comprehensively analyze the characteristics of annual temporal and spatial changes of soil moisture and its identity and opposition with the above-mentioned biotic and abiotic factors,explore the relationship between different biotic and abiotic factors and annual changes in soil moisture,and reveal the main controlling factors affecting soil water pools,the main findings and conclusions are as follows:(1)The research on plant community types,species composition,spatial distribution pattern and influencing factors shows that:in the complete watershed with lakes and wetlands as the core,the plant communities are mainly restored to four types.Factors such as topography and soil can explain 31.8%of the spatial variation characteristics of vegetation types and species composition;soil 0-20 cm fine sand and clay silt,60-80 cm and 80-100 cm fine sand,80-100 cm pH and salinity were the main controlling factors that determined the spatial distribution of plant communities and species composition(P<0.05);(2)Under the above-mentioned spatial distribution pattern of vegetation landscape,under the background of continuous drought,soil texture is the main controlling factor:0-20 cm surface coarse sand content and 20-40 cm clay silt content play a significant role in maintaining soil water retention;as the main controlling factor,the herb vegetation coverage of shallow root system began to significantly affect the soil moisture in the deep layer 60-100 cm,and the decline risk of the soil moisture retention function of the landscape system increased significantly;the spatial differentiation characteristics of soil moisture induced by the spatial distribution pattern of community types mainly occurred among zonal vegetation types with perennial dominant species.(3)Precipitation is the main factor that determines the seasonal variation of water in the desert wetland watershed system,and the soil water in the watershed exhibits obvious characteristics of dry season and wet season.Topography and soil under precipitation control the temporal and spatial changes,especially the spatial changes,of soil moisture in desert wetland watersheds.(4)In the desert steppe landscape including lake subsystems in the study area,the significant shrinkage and expansion of lake wetland area represent the transition from deficit to surplus of soil water reservoir at the scale of desert steppe landscape;under the background of continuous drought,with the lake as the center and radiating outwards,the core area of soil profile drought(water content<2%)always occurs in the construction area of arbor and shrub plantation in sandy habitat;In the restoration area,the shrubs and herbs with high content of fine particles in the soil of the habitat are mainly constructed,and the soil moisture is basically maintained at 4%-6%.(5)Based on the above-mentioned landscape-scale biological factors(characterized by plant community,arbor,shrub and grass coverage,diversity,stability,etc.),abiotic factors(soil texture,type,altitude)and soil moisture monitoring and other information comprehensive research shows that:in order to cope with the possible negative effects of extreme natural drought and precipitation events on the system,the consideration of vegetation coverage rather than community species allocation patterns is the key link for the sustainability of desert steppe vegetation restoration. |
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