Effects Of Sand-fixing Barrier On Vegetation,Soil And Biological Soil Crusts

China is one of the countries most seriously affected by desertification in the world.In recent decades,China's anti-desertification work has been actively carried out and has made great progress.Mechanical sand barriers,one of the most important engineering measures,are used to fix quicksand and restore vegetation and soil in the quicksand area,which in turn contributes to the formation of biological soil crusts.This thesis takes the Shapotou area on the southeastern edge of the Tengger Desert as an example,sees HDPE sand barriers and grass checkered sand barriers which deployed in different years as the research object.The effects of sand-fixing barriers on vegetation growth and soil nutrients in different years were analyzed.through the combination of field vegetation investigation,soil sample collection,and indoor sample analysis.It studied the community structure characteristics of fungal communities and cyanobacterial communities in biological soil crust under HDPE sand barriers.The conclusions were following :(1)The investigation results of vegetation in the two mechanical sand barriers in the Shapotou area show that the total number of plant species in the sand barrier is 5 families,12 genuses,and 12 species.Compared with the distribution of sporadic sand grains on mobile sand dunes,the setting of mechanical sand barriers can make the plant species increase.With the increase of the sand-fixing period,species in HDPE sand barriers and grass square sand barriers have increased.The number of species in HDPE sand barriers deployed in 2012 and 2010 was greater than that in sand barriers of the same period.(2)The species diversity index of the vegetation in the two types of sand barriers is relatively low and it increases with the time of sand barrier deployment.The diversity index and evenness index of HDPE sand barriers which installed in the same period are higher than that of grass sand barriers.The degree index is high,while the dominance index within the sand barrier and the diversity index and evenness index have opposite regular changes.(3)The study on the change of soil water content under two types of mechanical sand barriers in Shapotou area shows that the soil moisture content in the sand barrier increases first and then decreases with the increase of soil depth;at 0-40 cm,in the test area in August.Soil moisture is higher than that in September,but in 60-100 cm,the difference of the soil moisture between two months is not obvious.(4)The composition of soil particles in the two sand barriers in different soil layers is dominated by fine sand grains and coarse sand grains,and the average particle size of surface soil is larger than that of the underlying soil.With the period of sand-fixing increasing,fine sand grains and soil clay content increased,while coarse sand grains decreased.(5)The setting of sand barriers in the two materials makes the p H value of the soil decrease.The PH value of the grass sand barrier is lower than that of the HDPE sand barrier,which makes the total nitrogen of the surface soil(0-5 cm)in the sand barrier,the content of organic carbon,available potassium and available phosphorus content increase with respect to the surface of bare sand.Within 0-40 cm,the nutrient content of surface soil was higher than that of other soil layers;however,there was no significant difference in surface soil nutrient content between the two sand barriers.(6)A total of 49 OTUs were assigned to the biological soil crust fungus under the HDPE sand barrier.The phytozoa in the fungal community structure were mainly Ascomycota,accounting for 92.03% of the total.At the outline level,the dominant class is the sarcophagus,which account for a certain proportion with the sclerotinia related to the lichen and the Lichenina lichen.There were 41 species of eukaryotes in different stages of development of the crust,and there were 22 species of fungi in total,and there were 2species of endemic fungi in 2012.(7)There are 51 OTUs in the cyanobacteria under the HDPE sand barrier.In different developmental stages,there are 19 species of cyanobacteria and there are 16 cyanobacteria in total.In 2010,there was a unique cyanobacterium belonging to the cyanobacteria.The species of Microsporium is the most,accounting for 20.92%;Seaweed and Phytonema are also accounted for a certain proportion in the blue-green algae community.