The Screening And Identification Of Efficient Azotobacter In Iron Tailings Vegetation Restoration Areas And Analysis Of Nitrogen Fixation Effect

Investigation on soil microbial quantity has been carried out on basis of somevegetation restoration modes, such as direct vegetation restoration mode (Sabina pureforest mode, Amorpha fruticosa L. pure forest mode, Populus tomentosa pure forest mode,mixed forest mode), vegetation restoration mode based on the water conservationengineering, and covering with other soil for melioration restoration mode based onrefused waste and so on. The microorganism amount in sample plot I (newly picked irontailing in2012) is less than that in other sample plots, the reason is that the infertile tailingsand is bad for microbes to survive and reproduce as well as that the microorganismamount in iron tailing without any recovery measures is lower than that in normalconditions. On the contrary, restoration measures have been taken in another eight sampleplots and the microorganism amount increases quickly due to the improved growthenvironment.The microorganism amount tends to reduce with the deepening of the soil layer. In thesoil, bacteria occupy the largest proportion (96.6%on average) which is followed byactinomyces (2.9%on average) and fungus (0.5%on average). The study shows that themicroorganisms are predominant in iron tailing that lay a foundation for the screening andidentification of efficient Azotobacter.Totally, there were203strains screened from iron tailing, and48azotobacters withdifferent phenotypes were obtained from the number77Waksman medium. They wereserially passaged by plate streaking, and cultivated in liquid medium without nitrogen for48hours to enrich, then the activity of nitrogen fixation was measured by acetylenereduction assay, and the activities of45strains were between7.84nmol mg-1h-1and307.23nmol mg-1h-1. Two strains with higher enzyme activity were retained and namedDb1and Ec1, and the activities of enzyme were203.20nmol mg-1h-1and307.23nmol mg-1h-1respectively. The Ec1possess highest enzyme activity of in physiologicaland biochemical test and Biolog technical appraisal, and a conclusion can be got that theEc1belongs to Azotobacter.The inoculation experiment of screened efficient azotobacter was carried out onalfalfa, which shows that the plant growth conditions are better than that in control groups:the dry weight on the ground of the tested group increases by85%than that in control groups on average, the dry weight under the ground increases by87%, plant heightincreases by73%, number of lateral roots increases by67%, the longest lateral root is50%longer, and the main root is49%longer. Based on that, we could get a conclusion that Ec1strains can promote the growth of alfalfa plants.Through testing the contents of N, P, K and the soil enzyme activity in experiment ofpot planted alfalfa, the experiment studies the effect of the Ec1strains on the soil enzymeactivity and soil nutrient. The content of alkaline hydrolysis nitrogen was measured byalkali solution diffusion reaction, the content of available phosphorus was measured byMolybdenum-antimony colorimetry, the content of available potassium was measured byflame photometer, the activity of urease was measured by indophenol blue, the activity ofsucrose was measured by3,5-dinitrosalicylic acid, and the activity of phosphatase wasmeasured by disodium phenyl phosphate. The results indicates that the activities of soilenzymes are all higher than contrast group after inoculating Ec1, the activities of sucrose,phosphatase, and urease increase by0.058mg g-1d-1,2.14ug g-1h-1, and7.7ug g-1h-1respectively; the contents of Soil alkali-hydrolysable nitrogen, available phosphorus andavailable potassium changed along with the activities of soil enzymes, and the contents ofthem increase by24%,55%and13%respectively.It indicates that Ec1has played apositive role on the activation of soil and improved the activities of the soil invertase,urease and alkaline phosphatase and the contents of alkaline hydrolysis N, available K andP. The experiment reveals that Ec1has feasibility survive in the rough iron tailings habitatand efficient nitrogen fixation ability, it can be made into microbial agents in iron tailingswasteland restoration stage，Ec1has a broad application in the environmental recovery ofiron tailings with its significant azotification.