Profile Distribution Characteristics Of Soil Physical And Chemical Properties In Different Vegetation Types In Oasis Desert Transition Zone

The Oasis-Desert Ecotone is located between Oasis and Desert,which is an ecologically vulnerable zone with sensitive degradation trend and also the key region threatening the stability of oasis.This study mainly focuses on the Tarim Oasis Desert Transition Zone.Through the field investigation,collected seven different types of natural vegetation including Shrubs-Herbs,Arbor-Herbs,Arbor-Shrubs-Suaeda glauca Bunge Shrubs,Shrubs-Dry poplar,Arbor-Shrub-Herbs and Arbor,five soil profiles were taken at random around the sampling point in each vegetation type,and one soil layer was mixed in each of the five profiles at a depth of 0-100 cm.Therefore,the physical and chemical properties of soil samples in each vegetation type were determined,taking the mean value according to the soil physical properties of each vegetation type.The chemical properties were measured by mixed soil samples from the profile.The correlation and change trend of soil physical and chemical properties under seven different vegetation types were analyzed,and the differences and relationships among vegetation types,soil water and salt,physical and chemical properties were discussed.Finally,this study has concluded the following conclusions:(1)Under the seven vegetation types in the oasis desert transition zone,the species richness is the best under the Tree-Shrub-Herb vegetation type,and the shrub vegetation type has the best adaptability in the whole transition zone.The soil physical properties of different vegetation types have different distribution in different soil layers.The average soil bulk density of Shrub-Herb vegetation type is 1.51 g/kg,and the soil is the most dense compared with the other six vegetation types.The total porosity and capillary porosity of Shrubs-Dry poplar poplar vegetation type were 53.34 % and 47.29 %,and the soil is also the most porous and permeability compared with the other six vegetation types.The soil within 0-5cm under all vegetation types shows obvious looseness.The change trend of soil porosity with the increase of soil layer under different vegetation types is similar to that of soil bulk density.The soil bulk density is significantly negative correlation with the total soil porosity under seven vegetation types(P<0.01)。(2)The soil chemical characteristics of different vegetation types are as follows: under various vegetation types,the whole performance is that there is a correlation between soil total salt,soil p H and electrical conductivity,the correlation between soil organic matter and total nitrogen is obvious,but not with total phosphorus.The soil chemical influencing factors are different with different soil depths.It is found that under the vegetation type with tree Populus euphratica growth,The soil nitrogen content was significantly higher than that of other vegetation types without tree Populus euphratica growth.The vegetation type with arbor shows that the soil organic matter increases with the augmented of soil depth.There is a very significant positive correlation between the total salt content of soil and the conductivity of soil solution under the seven vegetation types,in which the correlation coefficient of arbor-shrub-Suaeda salsa vegetation type is 0.56,and the correlation number of the other six vegetation types is greater than 0.95,indicating that Suaeda salsa will affect the soil salt content and have a great impact on the total salt and conductivity of soil,Under the vegetation type without Suaeda salsa,the maximum soil water holding capacity and non-capillary water holding capacity showed a very significant positive correlation level(P<0.01).(3)In the oasis desert transition zone,there is a whole significant negative correlation between the total soil salt with herbaceous vegetation distribution and the soil water content in the seven vegetation types(P<0.05).The analysis indicates that the total salt of soil shows an inverse proportion within a certain range.The soil water content is an extremely important factor affecting the total soil salt,which reflects the dynamic change relationship between water and salt.The variation coefficients of soil moisture content and total soil salt varies greatly from different vegetation types.Under the Tamarix vegetation type,there was a significant negative correlation between soil available potassium,electrical conductivity and total salt(P<0.01).Under the other six vegetation types,there was a totally positive correlation between soil available potassium and electrical conductivity(P<0.01),and there was an extremely significant positive correlation between soil available potassium and total salt(P< 0.01).(4)Different plants in the study area had different tolerance to salt.Under the seven different vegetation types,the soil water content is between 1.72%-30.95% with the depth range of 0-100 cm,and the average moisture content is: T6>T1>T7>T4>T2>T5>T3.The soil moisture content was the highest when there were trees,shrubs and herbs vegetation types.The average content of total salt in 0-100 cm soil layer under each vegetation type is T5>T1>T6>T2>T7>T4>T3.The average salt content of soil under each vegetation type is greater than 1 g/kg except that the total salt of shrub and tree shrub vegetation types is less than 1 g/kg.(5)The vegetation types in the study area show different characteristics.In the depth range of 0-100 cm,the average bulk density of each layer of soil in the area where shrubs and herbs are distributed is the largest in the whole study area;In the area where trees and herbs are distributed,the average maximum water holding capacity in each layer of soil is the largest in the whole study area,which is higher than others;In the area with the distribution of trees,shrubs and Suaeda salsa,the average value of total phosphorus content in each layer of soil is the largest in the whole study area,while the average value of total porosity and total salt content is the smallest;Under the vegetation type with shrubs,the average value of soil capillary porosity is the largest while the average bulk density is the smallest;In the distribution area of Tamarix and Dry poplar,the average total salt content,p H and total porosity of each soil layer are the largest and the nitrogen content is the least in the whole study area;The average soil moisture content,electrical conductivity and organic matter content are the largest in the area where distribution trees,shrubs and herbs,in which the soil nitrogen content is the highest.