Abstract:[Background] Microbial fertilizers prepared with plant growth-promoting rhizobacteria (PGPR) are an important way to achieve sustainable agricultural development. [Objective] To systematically study the distribution of Bacillus velezensis FH-1 capable of promoting rice growth in complex soil systems and the mechanism of the strain in promoting rice growth on a spatial-temporal scale. [Methods] The rice seedlings were inoculated with B. velezensis FH-1, and rice seedling and rhizosphere soil samples in different layers were collected at different time points. The plant height and dry weight of rice seedlings were measured by a ruler and a balance, respectively. After DNA was extracted from the rhizosphere soil, 16S rRNA gene amplicon sequencing was performed to analyze the microbial community composition. Spearman correlation analysis was performed to study the correlations between rice and microorganisms. [Results] On day 0 after inoculation, there was no significant difference between the B. velezensis FH-1 (F) group and the control group (CK). The rice growth-promoting effect of group F became increasingly obvious over time. On day 20 after inoculation, the plant height and dry weight of rice seedlings in group F were 6.02% and 12.52% higher than those in group CK, respectively (P<0.05). During days 5–10 after inoculation, the colonization abundance of B. velezensis FH-1 in the 0–3 cm underground soil layer was 1.19%–2.64% higher than that in the 3–6 cm underground soil layer. During this period, B. velezensis FH-1 promoted rice growth by enriching Kineosporiaceae and Chitinophagales and promoting fumarate respiration in the 0–3 cm underground soil layer and enriching Bacillaceae and Phycisphaerae and enhancing nitrate ammonification in the 3–6 cm underground soil layer. During days 15–20 after inoculation, the colonization abundance of B. velezensis FH-1 in the 0–3 cm underground soil layer was 134%–139% higher than that in the 3–6 cm underground soil layer. During this period, B. velezensis FH-1 promoted rice growth by enriching Bacillus and Ilumatobacteraceae and promoting xylanolysis in the 0–3 cm underground soil layer and enriching Acidimicrobiia and Mycobacterium and boosting respiration of sulfur compounds in the 3–6 cm underground soil layer. [Conclusion] In the soil ecosystem, B. velezensis FH-1 promotes the early growth of rice seedlings by regulating the structure and function of the microbial community in the soil on a spatial-temporal scale.
