| In Northwest China,wind and sand activities are frequent,precipitation is scarce,and vegetation types are single.Jilantai salt lake is an important economic source in Alashan area.The development of salt lake has seriously damaged the surrounding ecological environment,making wind and sand raging and serious sand damage Tamarix chinensis shrub has the characteristics of large root system,strong branching ability,adapting to saline-alkali and arid environment.These characteristics of Tamarix chinensis can prevent the flow of sand invasion,so as to maintain the safety and stability of oasis ecosystem.Therefore,in this study,the Shurb size index(SSI)was constructed by combining field observation and indoor analysis,and the Tamarix chinensis shrub was divided into three grades: large,medium and small.The aim of this study was to reveal the overall configuration characteristics and sand heap morphology of different sizes of Tamarix chinensis shrub,and to explore the relationship between the overall configuration,branch component characteristics of Tamarix chinensis shrub and sand heap morphology,as well as the spatial heterogeneity of soil nutrients in sand heap.It provides a theoretical basis for improving the wind-sand hazard in desert areas and optimizing the configuration of shrub and branch system.The main conclusions are as follows :(1)The spatial form of Tamarix chinensis shrub is ellipsoid,dense and sparse in the middle of branches.The average lateral shadow area of the three shrub types was the largest at the height of 50-100 cm,the permeability of large shrub was the lowest at the height of 50-100 cm,and the permeability of medium shrub and small shrub was the lowest at the height of 30-50 cm.With the growth of Tamarix chinensis shrub,the shrub configuration indexes gradually increased.After the shrub grew to a certain size,the configuration indexes were adjusted.The branching length between different levels was gradually close,and the branching angle gradually changed into the angle of middle branch.The angle of outer branch and the first branch was small,so the growth of Tamarix chinensis shrub reached a stable state.(2)Tamarix chinensis shrub sand pile is convex semi ellipsoid.With the growth of Tamarix chinensis shrub,the morphological characteristics of sand pile gradually stabilized,and the configuration factors restricting sand pile morphology gradually changed from shrub canopy to shrub height.The canopy width of small and medium shrublands was significantly different from that of sandpile morphological parameters,while the height of large shrublands was only significantly different from that of sandpile short axis(P < 0.05,R = 0.931).During the growth of shrub,the lateral shadow area and porosity of the windward surface of shrub have always been important influencing factors of sand heap morphological parameters.(3)With the growth of shrubs,the spatial heterogeneity of soil nutrients in sand piles increased.The contents of soil nutrients(organic matter,alkali-hydrolyzable nitrogen,available phosphorus and available potassium)in 0-30 cm soil layer of small shrub increased by 30.94 %,-0.55 %,0.54 % and 19.96 %,respectively,compared with that of shrub empty land,medium shrub increased by 98.69 %,70.75 %,33.49 % and68.76 %,respectively,compared with that of shrub empty land,and large shrub increased by 49.12 %,26.87 %,71.63 % and 31.89 %,respectively.The distribution of soil nutrients in sand piles was significantly affected by the main wind direction.The maximum nutrient content in the range of shrub sand piles shifted to leeward slope,and the variation of soil nutrient content in windward slope was larger than that in leeward slope.(4)With the growth of shrub,soil nutrients gradually formed ’fertile island’.The enrichment rates of soil nutrients in large shrublands were 1.06–2.38(organic matter),1.10–3.05(alkali-hydrolyzable nitrogen),1.09–3.38(available phosphorus)and 1.01– 1.81(available potassium),respectively.The soil nutrient enrichment rate of the middle shrub sand pile was higher than 1,and the ’fertile island’ formed in the sand pile.The enrichment degree of soil nutrients in small shrub sand piles was small,and no’fertile island’ was formed. |
