Soil Moisture Of Different Vegetation Types And Dynamic Characteristics Of Leaf Area Index In Haba Lake Of Ningxia

The change of precipitation pattern caused by global changes has become an important ecological factor restricting vegetation construction in arid and semi-arid regions.Desert grassland area in central Ningxia is located in the transition area between loess Plateau and ordos platform.Geographical characteristics and climatic factors determine sparse vegetation and perennial soil water deficit.It plays an important role in the construction and renewal of regional vegetation.In ecological project construction,local xerophytic shrubs and mesophytic vegetation are often used as the main vegetation types to curb regional land degradation.Therefore,the study of vegetation-soil water-climate is of great significance to regional ecological restoration and vegetation construction.In this paper,different vegetation types(trees,shrubs and herbs)in Haba Lake National Nature Reserve in Yanchi County,Ningxia Hui Autonomous Region were taken as the research objects.A sample plot of typical vegetation types was set up by combining field investigation and satellite remote sensing data.Non-destructive sampling equipment such as automatic weather station,time-domain reflectometer and canopy analyzer were used.In order to provide theoretical and technical practice for the management of vegetation types in different regions,soil moisture and leaf area index(LAI)of different vegetation types in the study area were monitored by the method of regular fixed point continuous monitoring,and the temporal variation characteristics and their relationship were analyzed to explore the variation characteristics of precipitation and temperature in desert steppe.The results are as follows:(1)Precipitation characteristics.Yanchi County has a wide range of precipitation fluctuation from 1990 to 2022,with an average precipitation of 302.5mm in the past 30 years.The distribution of precipitation in each month is uneven and has an abnormal concentration,which mainly occurs in summer and autumn.In 2022,the precipitation in the growing season(April to October)accounts for 99.8%of the annual precipitation.In the study area,small precipitation events<5mm are the main events,and precipitation events≥10mm occur the least,but their contribution is large,which is the decisive factor of annual precipitation.(2)Temporal variation characteristics of soil water content.It can be divided into stable period(April-May),consumption period(June-July),replenishment period(August-September),and stable period(October)according to seasonal changes.Soil moisture content in stable period has a little recovery,and the recovery degree of soil moisture in April-May is not due to low precipitation.The soil water in the depletion period is mainly used for vegetation transpiration,soil evaporation and root water absorption.The precipitation in the replenishment period has an important effect on the annual water balance and the soil water cycle in the next year.(3)Spatial variation characteristics of soil water content.The vertical profiles of three different vegetation types were stratified according to the variation coefficient of soil moisture.For herbaceous and shrub plots,soil water change layer(0-40cm),soil water change layer(40-100cm),soil water stability layer(below 100cm);Tree plot:soil moisture change layer(0-40cm),soil moisture change layer(40-80cm),soil moisture stability layer(below 80cm).The variation coefficient of soil water decreased with the increase of soil depth.The variation of surface soil water content is very unstable,showing strong variability,while the deep soil water content basically does not change greatly,showing weak variability.The sudden increase of deep soil water variation coefficient is due to the influence of soil dry layer and groundwater level.(4)Variation characteristics of leaf area index.The leaf area index of different vegetation types was tree plot>shrub plot>herbaceous plot,and the coefficient of variation was tree plot(0.43)>shrub plot(0.30)>herbaceous plot(0.27).The overall trend of leaf area indices of different vegetation types with seasons showed a single-peak curve,which first increased,then remained relatively stable after reaching the maximum value,and then decreased.LAI peak appeared in August.(5)In the herbaceous,shrub and tree plots,the response degree of soil moisture at each soil depth to precipitation decreased with the increase of soil depth.The soil moisture below the 100cm soil layer of each vegetation type did not change significantly with the change of seasons,and the precipitation would have a great impact on the shallow soil moisture,with obvious seasonal changes.However,the deep soil moisture content and its change are more affected by vegetation itself.