Studies On Community Structure Of Nitrogen Fixing Bacteria In Rhizosphere Of Caragana In Western China

Caragana is a kind of shrubs which have drought resistance and cold resistance,and Caragana can hrive in barren soil.The nitrogen fixing bacteria in the rhizosphere of Caragana can be used for the normal growth and development of plants in the reverse environment.In this paper,a preliminary study was conducted on the community structure of nitrogen fixing bacteria in the rhizosphere of Caragana solated from Xilin Hot,Ordos,Alxa League,Wuhai and Yanchi.The characteristics of physiology and biochemistr are studied here.The results are as follows:1.21 nitrogen-fixing bacteria strains isolated from Xinlin Hot belonged to 6 groups and they are Rhizobium?Shinella?Mesorhizobium?Bradyrhizobium?Cupriavidus?Burkholderia?Arthrobacter.Arlhrobacler and Arthrobacter were dominant groups.20 nitrogen-fixing bacteria strains isolated from Ordos belonged to 10 groups and they are Oxalobacter?Rhizobium?Mesorhizobium?Chitinophaga?Dyadobacter?Arthrobacter?Neorhizobium?Sinorhizobium?Variovorax?Paenibacillus and Rhizobium and Arthrobacter were dominant groups.23 nitrogen-fixing bacteria strains isolated from Alxa League belonged to 6 groups and they are Arthrobacter?Rhizobium?Paracoccus?Pseudomonas?Novosphingobium?Paenibacillus and Pseudomonas was a dominant group.18 nitrogen-fixing bacteria strains isolated from Wuhai belonged to 9 groups and they are Bacillus?Microbacterium?Arthrobacter?Rhizobium?Phyllobacterium?Pseudomonas?Mucilaginibacter?Sphingobacterium?Paenibicillus,Arthrobacter was a dominant group.22 nitrogen-fixing bacteria strains isolated from Yanchi belonged to 13 groups and they are Sphingobacterium?Dyadobacter?Chitinophaga?Paenarthrobacter?Arthrobacter?Pseudomonas?Serratia?Ralstonia?Milsuaria?Inquilinus?Devosia?Agrobacterium?Phyllobacterium,Arthrobacter was a dominant group.According to the environmental factors,it is concluded that the different vegetation types and latitude may be the main factors causing the difference of nitrogen fixing bacteria community structure.2.The physiological and biochemical characteristics of 5 dominant strains were measured.The results showed that other strains can make gelatin liquefaction except for ALS14.Catalase activity was found in all tested strains.All of the strains had good use for glucose,maltose,lactose and mannitol.And all of the nitrogen fixing bacteria could grow on 1-3%NaCl medium.ALS14 had the best acid and caustic resistance.Other bacteria could grow between the pH values of 7.0-9.0.WH9,ALS14,E34 and XLHT26 can reduce nitrate to nitrite in the nitrogen cycle,and 7 strains can not produce indole and make indole reagent discolor.