| Haloxylon ammodendron community is the main plant community in the Gurbantunggut desert of the second largest desert in China.It plays a important role on windbreak and sand fixation,soil improvement and maintaining the oasis-desert ecological balance.However,the survey found that the H.ammodendron community in the western part of the Gurbantunggut Desert is in a state of severe degradation.The plants died a lot in the H.ammodendron community in the degraded area and the species in the community were scarce,so the cause of the degeneration of H.ammodendron community remains to be studied.In this study,three different degraded H.ammodendron communities in the western Gurbantonggut desert were investigated to compare and study the species composition,plant distribution,diversity characteristics,and soil physicochemical properties of H.ammodendron community.Combining with the physicochemical properties of soil,the relationship between the soil physicochemical properties and degradation of natural H.ammodendron community were analyzed.It is theoretical significance for the restoration of vegetation in the degraded areas of H.ammodendron and ecological protection in the northern Xinjiang's oasis area.The results are as follows:(1)There are 20 species of plants in all three species with different degrees of degradation.The composition of species in the community is relatively simple: there are 1 species of trees,5 species of shrubs,and 14 species of herbs,belonging to 8 genera and 19 genera.The species composition,species number,and species diversity index of H.ammodendron communities with different degrees of degradation were changed.As the degree of degradation increased,the number of plant species increased first and then decreased,while the species diversity index showed the first increase.And three different degrees of degradation of H.community are very dissimilar.(2)The H.ammodendron community in 19 plots in the degraded area is rare and its community structure is relatively simple.Shannon-Wiener of only 3 plots index were higher than 0.8.Simpson dominance index were all higher,and the Pielou index fluctuate significantly among plots.The highest coverage of vegetation in selected plots was 15.35% and the lowest was 0.99%.(3)The physicochemical properties of the soil profiles in different soil layers indicated that the average soil electrical conductivity,organic carbon,chloride ions,soil moisture content,and soil water storage all showed an increasing trend with increasing degree of degradation.With the intensification of degradation,the physicochemical properties of surface soil were higher than the physicochemical properties of deep soil.(4)Correlation analysis showed that there was a significant positive correlation between the total coverage of H.ammodendron communities in 19 plots and the physicochemical properties of 0-40 cm soil layers in the degraded areas.And there was a significant positive correlation between the coverage of the dead plants of H.ammodendron communities and the physicochemical properties of 0-40 cm soil layers.Principal component analysis revealed that soil physicochemical properties in 0-40 cm soil layer combined to inhibit community species diversity.(5)A comprehensive study suggests that the community structure of H.ammodendron in the Gurbantunggut Desert is simple and species composition is scarce,and it's undergoing a process of reverse succession.With the degeneration of H.ammodendron community,the H.ammodendron in the community is degraded through years of decomposition and erosion,witch resulted in the accumulation of mineral elements in the soil surface.As a result,the physicochemical properties of the surface soil deteriorate,which affects the seed germination and seedling establishment of different species in the community and the plant distribution and diversity composition,and in turn causes changes of the species diversity of H.ammodendron community.Eventually it will be lead to extensive degradation of H.ammodendron community. |
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