Abstract: In this study, three bacterial strains were isolated from the root nodules of Sophora davidii, Indigofera tinctoria, and Trifolium repens in the peak cluster-depression rocky desertification areas of Wenshan, Yunnan Province, which were coded as SWFU-B1, SWFU-B2, and SWFU-B3, respectively. By testing the morphological characters, physiological and biochemical properties and sequence analysis of 16S rDNA of the three strains, the similarities between the three strains and Rhizobium leguminosarum, R. anhuiense, R. oryzihabitans were 100%, 99.93%, and 99.78%, respectively. With a pot experiment, the three rhizobia strains were inoculated on faba bean under different drought stresses (normal moisture, mild drought, and moderate drought). There were four inoculation treatments: uninoculated (T0), inoculated with SWFU-B1 (T1), inoculated with SWFU-B2 (T2), and inoculated with SWFU-B3 (T3). The effects of inoculation with three rhizobia strains on faba bean were quantified by measuring several variables, including plant height, stem diameter, nodule number, leaf area, antioxidant enzyme activity, osmotic adjustment substances and malondialdehyde content. With the severity of drought, the growth of faba bean slowed down, and the number of root nodules decreased significantly. Compared with no inoculation, under the same soil water content, the growth index of faba bean inoculated with rhizobia was better, showing a significant growth-promoting effect. Under moderate drought, plant height in T2 was 68.10% higher than that in T0, and the number of root nodules was 23.53% higher than that in T0. Under the same drought stress, compared with the T0 treatment, there were higher antioxidant enzyme activity and osmotic adjustment substance content in inoculated faba bean. The SOD activity of T1 reached 123.44 U·g^-1·min^-1, being 50.83% higher than T0. The proline content was 20.54 μg·g^-1, being 72.32% higher than T0. Those results indicate that inoculating rhizobium can improve drought resistance of faba bean. Under the same drought stress, the malondialdehyde content of faba bean inoculated with rhizobium was significantly lower than that of no inoculation. In moderate drought, the malondialdehyde content of T1 was 33.33% lower than that of T0, indicating that the inoculation of rhizobium reduced the damage of drought to cell membrane of faba bean. The drought resistance of faba bean in the experimental groups was T1>T2>T3. The faba bean inoculated with strain SWFU-B1 showed the best drought resistance. In conclusion, under drought stress, inoculating rhizobium can significantly promote the growth and drought resistance of faba bean. This study provided a reference for restoration method and high quality strains for vegetation restoration in rocky desertification area.

Key words: peak cluster-depression rocky desertification, rhizobia, growth-promoting, drought resistance.