| Endophytic nitrogen-fixing bacteria was an efficient nitrogen-fixing system, it was different from classical symbiotic nitrogen fixation and joint nitrogen fixation which were newly discovered in recent years. Endophytic nitrogen-fixing bacteria was living in non-leguminous plants, avoiding the inhibition of nitrogen compound and the competition of indigenous microbion, showing a higher efficiency of nitrogen fixation. At the same time, it has a wide range of biological and ecological role of IAA-Producing activity, solubilizing phosphate activity and enhanceing plant disease resistance, and has important application value in improving host nutrition and competitiveness, enhanceing the host of biotic and abiotic stress resistance and promoting the ability to adapt their environment. In this study, the microbial population, community composition and biological activity in rhizospheric soil of several kinds of typical dominant desert plants at the lower reaches of Tarim River, Xinjiang were studied, revealing the interaction between plants and rhizosphere microorganisms, and the affection of plant genotype to the rhizosphere effect. On this basis, isolated the endophytic bacteria from Tamarix ramosissima and Lycium ruthenicum, selected the varieties of functions Plant Growth-Promoting endophytic bacteria strains, These strains had the quality of high nitrogenase activity, solubilizing phosphate activity and IAA-Producing activity, in order to lay the foundation for creating and appling the multifunctional inoculant with the conservation and restoration of desert vegetation. The main results showed:The rhizospher of the desert plants were quite different from non-rhizosphere in microbial population and composition, and had various rhizosphere effects, shrubs was superior to the herbs in rhizopheric effects. Several desert plants at the lower reaches of Tarim River exerted more obvious positive rhizosphere effects , R/S values reached from1.26 to 150.42, such as Lycium ruthenicum,Tamarix hispida,Karelinia caspica and Halostashys caspica, Lycium ruthenicum was the best one, its R/S values reached to 150.42. On contrary , Alhagi sparsifolia, Apocynum venetum and Hexinia polydichotoma showed negative rhizosphere effects. The physiological groups of ammonifiers and cellulosed ecomposing bacteria also exhibited remakable positive rhizosphere effect, however the nitrobacteria could not be examined.The desert plants growing could improve activity of urease and alkaline phosphatase in the rhizospheric soil. However, the effects of different desert plants on soil respiration intensity and the activity of the hydrogen peroxide showed different.Fifty-eight of endophytic nitrogen-fixing bacteria strains were obtained in Lycium ruthenicum and Tamarix ramosissima, and the nitrogenase activity is from 0.26 to 388.58 nmolh-1mL-1. It is proved that endophytic bacterial strains with high nitrogenase activity can be isolated from desert shrubs. Tested the all endophytic bacterial strains isolated indicates that 25 strains have solubilizing phosphate activity by measuring activity of phosphate solubilization, its magnitude is from 5.457 to 24.212μgmL-1, 25 strains have the higher capacity to secrete auxine IAA and the productivity quantum of IAA is from 0.114 to 1.392μgmL-1, and 13 strains have multi-promoting function including azotification, solubilizing phosphate and the capacity to secrete auxine IAA. And the promoted function of the EB20-THQ strain among is stability and predominance.Using the immune electronic microscope dyeing to localization the field planting and transimission of the endophytic diazotrophic bacteria EB20-THQ in the desert shrubs and indicates that the EB20-THQ strain can invade into the host of root. Determinating the whole 16SrDNA sequence and analysising the phylogenesis, the 5 endophytic diazotrophic bacteria strains of high growth-promoting belong to Klebsiella.
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