Vegetation Community And Soil Characteristics Of Degraded Tamarix Ramosissima Nebkhas In Minqin Oasis-desert Ecotone

The health of oasis-desert ecotone is extrmely important to the ecological security of oasis.However,due to human disturbance and the change of natural environment,the vegetation of ecotone began to decay and die in large areas,and the effect of desertification and wind erosion is serious on the edge of oasis,which directly threatens the survival and development of local people.Tamarix ramosissima nebkhas is the main sand-fixing vegetation in the west and northwest margin of Minqin Oasis,however,due to the underground water level and the drought decline,the phenomenon of reducation and fragmentation in the oasis marginal area,it also has seriously affected the local security in recent years.In view of this,we used the method of space-time substitution way commonly used in ecology and selected different degradation degree of Tamarix ramosissima nebkhas,via field sampling and indoor analysis,studies the change regularity of vegetation,nebkhas,soil physicochemical properties and biological characteristics in the process of the degradation of Tamarix ramosissima shrub.It could provide scientific basis for the restoration and conservation of Tamarix ramosissima nebkhas in this area.The results show that:(1)With the increase of degradation degree,the characteristics of the vegetation of Tamarix ramosissima are as follows: the coverage and new length decreased,rate of dead branch,plant height and Patrick richness index increased.Changes of the relevant parameters of the sand pile are as follows: the area damaged by surface wind erosion rapidly increases,and the length perpendicular to the main wind axis increases first and then decreases.the length parallel to the main wind direction axis and surface area gradually increase;the height increase.(2)The soil physicochemical and biological characteristics with the aggravation of degeneration,show that the clay and fine sand particles increased,silt sand first increase then decrease,coarse sand grains increased.The mean grain size and absolute value of skewness showed an increasing trend,sediment composition gradually became thicker,and the sorting of sediments in the shrubs became better.and tend to normal distribution.The bulk density increases,the soil water content decreases,and the changes within the shrub also tend to be stable.The total salt content and electrical conductivity,Ca2+,K+,Na+,Cl-,SO42-,available P content were all decreased.The changes of p H value and HCO3-,Mg2+,total P content were insignificant.The content of available N and cation exchange capacity,total N,organic matter increase first and then decrease.The number of microorganisms dropped and the enzyme activity decreased in soil.(3)With the change of depth,the surface of soil grain size is coarse,the separation is good,the lower layer is fine,the sorting is poor,in addition to individual,the soil water content and microbial quantity,enzyme activity decreased,generally,salt and nutrient content higher at 0-5cm or 5-10 cm.(4)The difference among the different degrees of degradation is as follows: as a whole,the difference between non-degradation and degeneracy is significant,and with the intensification of the degree of degradation,the difference among the shrubs or soil layers is gradually significant.The correlations among different degradation degrees are as follows: The correlation between the vegetative parameters of shrub vegetation and sand dune is significant.In addition to individual indicators,the relationship between soil particle size and soil physicochemical properties,soil enzyme activity,soil microbes is significant.The connection within the nature is also close.(5)The characteristics of soil in the degraded Tamarix ramosissima shrubs can be attributed to four main components,in order of soil moisture and biological characteristics and nutrients,salinity,soil structure and acid-base environment,the variance contribution rate were 28.566% and 22.386%,15.258%,12.565%.To sum up,in addition to individual indicators,both vegetation and soil of the Tamarix ramosissima shrub have deteriorated or declined,and the relationship between the factors is close,in the oasis-Desert ectone of the Minqin Lake region at the process of degeneration.The degradation of Tamarix ramosissima shrub is the result of soil moisture and biological characteristics as dominant factors,comprehensive effects of nutrients and salinity,soil structure.Therefore,it is the key to further improve the depth of groundwater level to the critical water level which can be utilized by the Tamarix ramosissima by supplying groundwater.In this context,some new materials which can comprehensively improve the soil environment of the nebkhas are also artificially modified to speed up the natural repair rate of degraded shrub.