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Endophytic nitrogen-fixing bacteria which could improve the competitiveness and nutrition, enhance stress resistance of hosts had great potential, and showed a good prospect in ecological restoration. In this study, the strains which were isolated from the roots of Tamarix ramosissima Ledeb. and Lycium ruthenicum Murr. at the lower reaches of Tarim River. Study on adaptability to environmental factors, measure the characters of colonization and conduction and its propagation of culture parameters. On this basis, the effect of strain on stress drought and growth of desert shrub were studied to provide a scientific basis and technological support for the exploring the construction, creation and application nitrogen-fixing of desert shrubs, growth promoting, stress resistance of multifunction inoculation.The main results showed:Five strains (DENB2, DENB6, DENB19, DENB20, DENB55) isolated from the root of Tamarix ramosissima Ledeb. and Lycium ruthenicum Murr. could grow and exhibit nitrogenase activity under the wide range of temperature 15-40℃and pH 5.0-10.0. The strains showed strong stress resistance, because they could also tolerate to sodium chloride concentration of 0.1%-5.0%, NH4+ concentration of 0.5-4.0mmolL-1 and a range of -0.3～-0.15mPa osmotic potential respectively. But there was difference among the stains in their stress resistance, and the stress resistance of strain DENB20 was the stronggest.The seeds of Tamarix ramosissima Ledeb.were soaked with the strain DENB20, which could infect roots and transfer to the organization of branches and leaves, and the roots were the best colonization. Under the condition of normal water supply, the speed of bacteria proliferation was faster than the strain that was under the condition of drought stress. Drought stress would reduce the proliferation rate, volume and stability. The impact increased with the increase of stress.Under drought stress, the strain could fix nitrogen, improve seed germination, promote the absorption of potassium and increase the organic matter and available nitrogen of soil. Under the condition of normal water supply, mild, moderate and severe drought stress, the fresh weight of endophyte-infected plants were increased 19.6%,13.3%,3% and 6.1%, compared with endophyte-free plants, respectively. The dry weight biomass of endophyte-infected plants were increased 32%,27%,5.9% and 60%, compared with endophyte-free plants, respectively. To some extent, growth losses were reduced due to drought stress.The activities of SOD, CAT of endophyte-infected plants were higher than those of endophyte-free plants. The more significant the activities were, the strongger the drought stress was. At the same time, the contents of MDA and Pro in endophyte-free plants were higher than those of endophyte-infected. The decreasing of cell membrane permeability could reduce the the damage of lipid peroxidation level, enhance root activity, reduce the impact of plants under water stress and improve plant drought resistance.After a single factor and multifactor orthogonal experimental design,the optimum condition of strain ferment was:malic acid 10g·L-1, sodium nitrate 0.05g·L-1, KH2PO40.2g·L-1, MgSO4·7H2O 0.2g·L-1,NaCl 0.2g·L-1, CaSO4·2H2O 0.1g·L-1, CaCO35.0g·L-1, pH=5, culture temperature was 35℃,culture time was 24h.
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