| Summary: | Phytase plays an important role in crop seed germination and plant growth. In order to fully understand the plant growth-promoting mechanism by <i>Rahnella</i> <i>aquatilis</i> JZ-GX1, the effect of this strain on germination of maize seeds was determined in vitro, and the colonization of maize root by <i>R. aquatilis</i> JZ-GX1 was observed by scanning electron microscope. Different inoculum concentrations and Phytate-related soil properties were applied to investigate the effect of <i>R. aquatilis</i> JZ-GX1 on the growth of maize seedlings. The results showed that <i>R. aquatilis</i> JZ-GX1 could effectively secrete indole acetic acid and had significantly promoted seed germination and root length of maize. A large number of <i>R. aquatilis</i> JZ-GX1 cells colonized on the root surface, root hair and the root interior of maize. When the inoculation concentration was 10<sup>7</sup> cfu/mL and the insoluble organophosphorus compound phytate existed in the soil, the net photosynthetic rate, chlorophyll content, phytase activity secreted by roots, total phosphorus concentration and biomass accumulation of maize seedlings were the highest. In contrast, no significant effect of inoculation was found when the total P content was low or when inorganic P was sufficient in the soil. <i>R. aquatilis</i> JZ-GX1 promotes the growth of maize directly by secreting IAA and indirectly by secreting phytase. This work provides beneficial information for the development and application of <i>R. aquatilis</i> JZ-GX1 as a microbial fertilizer in the future.
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