Effects of Bacillus on Continuous Cropping of Sugar Beets and Their Rhizosphere Microbial Community

Background and Aims Sugar beet is a vital sugar-producing crop, and continuous cropping poses a major threat to its growth, leading to a decline in its yield and quality. This study aimed to investigate the effects of two bacterial agents, Bacillus subtilis and Bacillus mucilaginosus , on the growth, soil physicochemical properties, and rhizosphere microbial community of sugar beet seedlings. Methods We employed pot experiments and amplicon sequencing to analyze the impact of applying two different Bacillus agents on the microbial community structure in the rhizosphere soil of continuously cropped sugar beet and explore the microbial composition, environmental driving factors, and potential functions present within the microbial communities. Results The results showed that both Bacillus agents and their combination significantly promoted the growth of continuous cropping sugar beet seedlings, reaching or even surpassing the levels observed in crop rotation, improved soil pH, and enhanced soil environment. High-throughput sequencing analysis of the rhizosphere soil revealed that all Bacillus treatments induced changes in the diversity and structural composition of the rhizosphere microbial community, and significantly increased the relative abundance of Proteobacteria, thereby enriching beneficial microorganisms such as Pseudomonas , Novosphingobium , and Sphingomonas compared with that in the control group. Additionally, the application of Bacillus inoculants significantly enhanced the nitrate respiration, nitrogen respiration, and chitinolytic functions. Conclusion These two bacterial agents optimized soil physicochemical properties and improved the rhizosphere soil microbial community structure, promoting sugar beet seedling growth and effectively mitigating the negative effects of continuous cropping.