| Desertification is an important environmental problem in the world.It seriously affects and plagued the survival of all mankind and the sustainable development of society.C hina is one of the most serious countries affected by land desertification in the world.The prevention and control of desertification is very important.The biological crust is a layer of special surface structure formed mainly by the interaction of bacteria,algae,lichen,moss and soil particles in the soil surface development,which has played a significant role in the wind and sand,regional ecological environment changes and material energy exchange.MU Us sand and Shapotou area are affected by desertification,Desertification prevention and control work carried out earlier,and soil biological crust is well developedin the region.In this study,the four enzyme activit ies(soil?-glucosidase,soil urease,soil alkaline phosphatase and soil aryl sulfatase)were measured in the soil of Mu Us sandy land,screening high-yield extracellular polysaccharides bacteria isolated from Mu Us sandy land and Shapotou area,and studing soil crust effect of high-yield extracel ular polysaccharides bacteria.Research indicates:The results showed that vegetation has a significant effect on the enzymatic activity of sand.Under vegetation cover,the soil-?-glucosidase activity of 0-5 cm layer was higher than that of sandy land,while under 5 cm,the effect of vegetation on soil enzyme activity was less,The activity of soil aryl sulfatase,soil urease and soil alkaline phosphatase were higher than the flowering land.In the same vegetation and the same planting age,The soil-?-glucosidase activity on the part did not show a significant decrease with the increase of soil depth but on the whole showed an decrease trend,The soil aryl sulfatase,soil urease and soil alkaline phosphatase all decreased with the increase of soil depth.Under the same soil depth and the same planting age,different vegetation types had some influence on soil enzyme activity and mainly showed shrubs>grassland>trees.Under the same sand depth and the same vegetation type,different vegetation planting ages had some influence on the soil enzyme activity,and mainly showed that the largest in 1960,followed by 1985 or1990.A total of 48 strains of extracellular polysaccharides were screened out which isolated from Shapotou and Maowusu sandy land at first screening.Ten strains of high yield extracellular polysaccharide were re-screened out by phenol-concentrated sulfuric acid method,andrespectively were J3,J5,J7,J13,J16,24-1,2-3,28-19,27-20,38-19.The highest yield of exopolysaccharide was J3 and 24-1,and the production respectively was 189,833?g/m L and 193.167?g/m L.In the alkali resistance,10 strains of bacteria can grow in the pH 7-9,part of the strains can grow at pH 10,and all of are alkaline or basophilic microorganisms,andthe range of the most appropriate growth pH are 6-8.In salt tolerance,10 strains of bacteria have a certain salt tolerance,and all of are mild or moderate halophilic microorganisms,the optimal growth of salt concentrations are 1%or 5%.In the morphological aspects,10 strains of bacteria were all bacillus,some strains have flagella and some not smooth on the surface.J3,J5,38-19 are the Gram Negative bacteria,the remaining are Gram-positive bacteria.Indoor simulation test showed that spraying bacteria has a clear crust effect,are able to form more than 9 mm crust,the thickest reached 13.209 mm,and the hardness was significantly enhanced,the average maximum hardness is 20.66 kg/cm~2.The crusts formed by spraying the bacteria have a certain water holding capacity,and water holding capacity of crust enhanced while water permeability decreased.In addition,the bacteria sprayed on the sand has a certain viability,can survive in the sand and are dominant bacteria. |
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