Study On The Relationship Between Vegetation And The Characteristics Of Soil Dry Layer On The Typical Slope Of Mountain Areas Of Southern Ningxia

Since the implement of '813' ecological improvement construction,vegetation planting in mountain areas of southern Ningxia has increased vegetation coverage,reduced soil erosion,and improved the regional environment,but the problems of soil desiccation has caused some vegetation has declined or withered,so the relationship between the dried soil layer and the vegetation system needs to be studied.In this paper,Armeniaca sibirica,Populus davidiana,Ulmus pumila,Hippophae rhamnoides,Caragana Korshinskii,Artemisia scoparia,Arundinella hirta,Sporobolus fertilis,and Zea mays were selected as the research objects in the slopes of mountain areas of southern Ningxia,and got layered soil samples and corresponding plant samples from 0-600 cm layer by layer,and analyzed the vertical profile distribution characteristics of soil moisture.The initial depth of dry layer,dry layer thickness,the average moisture content in dry layer,drying index,relative deficit index of soil moisture were used to evaluate soil desiccation intensity and water deficit degree and used redundant analysis to analyze impact factors.At the same time,the species composition in the study area was investigated by sample method,and the suitability of different plantation vegetation communities was evaluated by using Patrick,Shannon-Winner,Simpon,and Pielou indexes.Finally,the index system of dry soil layer and vegetation system was constructed,and the weights of each index was determined by using the analytic hierarchy process and entropy weight method.The coupling characteristics of vegetation and soil layers in the study area were revealed by coupling degree model and coupling coordination model.The results showed that:(1)The A.sibirica,P.davidiana,U.pumila,H.rhamnoides,C.korshinskii kom,A.scoparia,A.hirta steud,S.fertilis,Z mays and their soil physical and chemical properties were affected by natural and human factors,and showed differences in spatial distribution.Moreover,the degree of spatial variation and autocorrelation and autocorrelation coefficient under different lag distance were different,and the optimal semi-variance fitting function of soil physicochemical properties also showed obvious differences.(2)The average drying index during the range of 0-600cm of A.sibirica,P.davidiana,U.pumila,H.rhamnoides,C.korshinskii,A.scoparia,A.hirta steud,S.fertilis,Z mays were 63.48%,91.88%,95.17%,87.67%,75.72%,157.81%,186.57%,139.06%,and 156.02%respectively.The average relative deficit index of soil moisture of them were 0.68,0.59,0.52,0.41,0.66,0.00,-0.06,and 0.15 respectively.The average drying index during the range of 0?600cm of armeniaca sibirica of 3,17,23,35a were 184.36%,99.87%,74.60%,and 59.15%respectively.The average relative deficit index of soil moisture of them were-0.16,0.29,0.45,and 0.53 respectively.Trees and shrubs experienced soil moisture deficits and moderate to light soil desiccation(3)There were 51 species of plants in the study area,including 8,2,39,and 2 species of trees,shrubs,herbs and crops,belonging to 48 genera and 20 families.Among them,12 species and 10 genera of gramineae plants,9 species and 6 genera of asteraceae,and 7 species and 7 genera of legumes accounted for 23.53%,17.65%,and 13.73%of the plant species in the study area respectively.The abundance index and diversity index showed herb>shrub>arbor,while the dominance index and biomass showed opposite trends.(4)The comprehensive weights of soil bulk density,clay,silt,saturated water content,capillary porosity,forming depth of desiccated soil layer,thicknesses of desiccated soil layer,soil desiccation index,compared soil water deficit index,organic matter,total phosphorus,total nitrogen,and total potassium were 0.0480,0.0393,0.0417,0.0533,0.0736,0.0542,0.0165,0.1908,0.0814,0.0617,0.0784,0.0327,0.0654,and 0.1633 respectively.The comprehensive weights of Tree height,DBH,crown width,biomass,organic matter,total phosphorus,total nitrogen,total potassium,richness index,diversity index,and dominance index were 0.0341,0.0510,0.0550,0.0915,0.0594,0.0641,0.0846,0.0829,0.1968,0.1983,and 0.0826 respectively.Main reasons leaded to the soil desiccation in the research area were vegetation type,stand age,DBH,crown width,tree height,and soil texture.(5)The arbor land and shrub land were on the verge of dysfunctional development,and the soil dry layer lags behind the development.Abandoned farmland and grassland were all in the mode of barely coordinated development,and vegetation and soil dry layers developed simultaneously.Agricultural land was a primary coordinated development mode,and the vegetation and soil dry layers developed simultaneously.