[Objective] The paper aims to explore the effect of inoculating plant growth-promoting rhizobacteria (PGPR) on the rhizosphere soil of Fraxinus chinensis under different salt stress conditions

and to clarify the improving effect of PGPR on salinity tolerance of F. chinensis and provide theoretical support for the extension of PGPR in salt stress environment.[Methods] We used a pot experiment covering different salt stresses[light salt stress(LS)

moderate salt stress(MS)

and severe salt stress(SS)] and corresponding inoculating PGPR to evaluate the effects of different treatments on the biological characteristics of rhizosphere soil and growth of F. chinensis.[Results] The microorganism population

the contents of microbial biomass carbon and microbial biomass nitrogen

the activities of urease enzyme

polyphonic oxidase enzyme

catalase enzyme and invertase enzyme under salt stress conditions were significantly decreased

and the decreased magnitude become larger and larger along with the increasing salt stress

whereas the corresponding indexes showed an increasing trend after inoculating PGPR. The populations of bacteria

actinomycetes and total microbial by LS+P treatment achieved the maximum value

increased by 14.64%

24.01% and 17.04% compared with CK

respectively

and the activities of urease enzyme

polyphonic oxidase enzyme and invertase enzyme had no significant differences between LS+P and CK treatments

while they significantly increased compared with the other treatments. Meanwhile

the root volume

total absorption area and active absorption area also demonstrated a trend of decreasing as the degree of salt stress increased

but the corresponding indexes increased after inoculating PGPR. The active absorption area in LS+P treatment markedly increased by 15.97% in comparison with CK. Additionally

compared to CK

the ground diameter and plant height significantly decreased in the treatments of different degrees of salt stress

while an opposite trend was presented after inoculating PGPR. And the ground diameter and plant height in LS+P treatment had no significant differences compared with CK

whereas they significantly increased compared with the other treatments.[Conclusion] The inoculating PGPR under light salt stress could significantly improve the biological characteristics of rhizosphere soil and growth of F. chinensis

and the effect was significantly higher than inoculating PGPR under moderate and severe salt stress.