Objective: Lycium ruthenicum is a type of perennial halophyte shrub, which is wildly cultivated in Xinjiang, promoting both the local economic development and environmental protection. In order to obtain strains with salt-alkali tolerance and growth promoting characteristics, the saline-alkali tolerant rhizosphere bacteria of L. ruthenicum were isolated from the rhizosphere soil of L. ruthenicum in the saline-alkali land of Shanshan, Xinjiang.
Methods: The rhizosphere microorganisms were isolated by gradient dilution coating method, and the morphology and growth characteristics were then observed by Gram staining and plate scribing method. Several stable strains were selected for 16S rRNA gene sequence alignment. The above strains were screened in the medium with salt mass fraction of 2%~25% and pH of 5~12, and their desalination and alkali removal characteristics were studied. The growth promoting characteristics were studied by qualitative and quantitative methods of nitrogen fixation, phosphorus dissolution, indoleacetic acid (IAA) production and iron carrier production, and pot experiments were carried out.
Results: 110 rhizosphere microorganisms were isolated from the rhizosphere soil of L. ruthenicum by gradient dilution coating method. The colony morphology and growth characteristics were observed by Gram staining and plate scribing method. 37 strains were selected for 16S rRNA gene sequence alignment. The results showed that 37 strains belonged to 9 genera, of which Bacillus was the dominant genus. Among them, 10 rhizosphere bacteria could grow in the medium with salt concentration of 2%~20% and pH of 5~11. At 36 h, the desalination and alkali removal efficiency was the best, and the desalination and alkali removal efficiency of strain HQY8 reached 75% and 42%. 10 strains of saline alkali tolerant rhizosphere bacteria could also grow in nitrogen-free medium of Ashby and draw birth length curve. The concentration of dissolved phosphorus was between 28.20~52.63 mg/L. Strain HQA2 could produce 54.21 mg/L IAA and the best iron carrier at 60 h. The diameter of the yellow halo around was 37.25 mm. Compared with the blank control group, the growth of L. ruthenicum seedlings in the negative control group was severely inhibited, and the fresh weight, dry weight, plant height, leaf number and chlorophyll content of L. ruthenicum were reduced by 83.5%, 78.0%, 46.1%, 41.3% and 12.4%, respectively, compared with the blank control group (P<0.05).
Conclusion: The 10 strains of saline-alkali tolerant rhizosphere bacteria screened could promote the growth of L. ruthenicum seedlings to varying degrees. Among them, HQA8, HQA9, HQX56, HQX34 and HQA2 have the higher ability for promoting the growth of L. barbarum seedlings than that of HQA14, HQY4, HQY5, HQA4 and HQK4. These results could provide excellent strains for the development of biological fertilizer and the improvement of extreme soil environment.