Effects of different NaCl levels on the growth of rhizobia. The four tested Bradyrhizobium strains were separately inoculated onto liquid YMA medium containing 0.0017 (CK), 0.1, 0.2, 0.3, 0.35, 0.4, or 0.5 M NaCl and further incubated at 28 °C and 180 rpm. The optical density (OD) of the cultures was recorded at 600 nm after 8 days of NaCl treatment. Each bar represents the mean of four biological replicates with standard error. An individual flask was considered one biological replicate. The same lowercase letter indicates no significant difference at p < 0.05 (Duncan’s test) in RJS9-2 among different treatments. The same uppercase letter indicates no significant difference at p < 0.05 (Duncan’s test) in LZ3-2, BS1-1, and PN13-3 among different treatments, respectively. Due to the same results from Duncan’s test of LZ3-2, BS1-1, and PN13-3, only one group of representative uppercase letters is showed in the figure.