Effects of Broccoli Rotation on Soil Microbial Community Structure and Physicochemical Properties in Continuous Melon Cropping

The limitations and weaknesses of continuous melon cropping have worsened in recent years. A melon–broccoli rotation can possibly alleviate the problems associated with melon monoculture; however, the underlying mechanisms and their impact on the rhizosphere’s soil microbial community remain unclear. Thus, high-throughput sequencing was used to evaluate the rhizosphere soil’s microbial community’s relative abundance and diversity under melon–broccoli rotation and continuous melon monoculture cropping systems. We found that relative fungal and bacterial diversity and richness increased while fungi relative abundances, such as Fusarium spp. were significantly decreased under broccoli rotation. During continuous cropping, enriched Acidobacteria and Streptomyces spp., Sphingomonas spp., and Pseudomonas spp. were identified, which play important roles in alleviating melon continuous cropping obstacles. The soil under continuous cropping was rendered acidic, underwent secondary salinization, rapidly accumulated soil organic carbon and nitrogen, and lost abundant phosphorus and potassium. In contrast, broccoli rotation partially mitigated these negative physicochemical responses. Redundancy analysis revealed that the soil pH, soil soluble salt content, and soil organic carbon were linked to structures of the soil bacterial and fungal community. Melon–broccoli rotation could effectively equilibrate the soil microenvironment and overcome the challenges and deficiencies associated with continuous melon cropping.