Abstract: By using PCR-DGGE technique, this paper studied the effects of different concentration (0, 25, 50, 100, and 200 mg·kg^-1 soil) cinnamic acid on the bacterial DNA polymorphorism in rhizosphere soil of cucumber seedlings under the stress of 292.5 and 585 mg NaCl·kg^-1 soil. At all growth stages of cucumber seedlings, treatment 50 mg·kg^-1 of cinnamic acid had the similar band numbers and band gray scales in DGGE profiles to treatment 0 mg·kg^-1 of cinnamic acid, but the diversity index, richness index, and evenness index were the highest; while in treatments 100 and 200 mg·kg^-1 soil of cinnamic acid, the band numbers and band gray scales decreased, and the diversity index, richnes index, and evenness index were lower. Our results demonstrated that low concentration cinnamic acid relieved the salt stress on soil microbes, while high concentration cinnamic acid aggravated the stress. The cloning and sequencing results showed that the main bacterial groups affected by salt stress were uncultured bacterial species, α-roteobacteria, β-proteobacteria, and γ-proteobacteria, and a few were Firmicutes, Acidobacteria, and Actinobacteria.

Key words: salt stress, cinnamic acid, PCR-DGGE, soil bacteria, regolith, earth road in loess area, runoff yield, sediment yield, simulated rainfall.