The continuous cropping can restrict the large scale and intensive cultivation of muskmelon, and the use of Trichoderma preparation to alleviate the negative effects is an effective mean. Although the impact on rhizosphere soil microbial communities and metabolites after applying Trichoderma are still unclear. In this study, we applied the fermentation broth of Trichoderma viride T23 to muskmelon under continuous cropping, collected rhizosphere soil samples at 60 days after transplantation, and investigated the changes in the microbial communities and metabolites of muskmelon by using high−throughput sequencing and metabolomic analysis, respectively. The results showed that T. viride T23 could effectively reduce the disease index of muskmelon wilt (65.86 to 18) and significantly increase the soil pH value (6.06 to 6.40). Trichoderma viride T23 induced drastic shifts in the richness, structure, and composition of rhizosphere microbial communities, and Proteobacteria, Bacteroidetes, and Actinobacteria were the dominant bacterial phyla. Bioactive substances such as scopoletin, erythronic acid, and palmitic acid were significantly upregulated in the rhizosphere soil, which enhanced soil activity. Overall, T. viride T23 resolves the continuous cropping limitation in muskmelon by improving soil physicochemical properties, elevating the biomass and diversity of soil microbial communities, and stimulating the production of soil active substances.
The autotoxins of muskmelon are one of the most important reasons for the continuous cropping obstacle of muskmelon, of which the main components are phenolic acids. Phenolic acids can inhibit the growth and development of muskmelon plants. The purpose of this study was to screen the strains that can degrade phenolic acids in soil. Using phenolic acids as the sole carbon source, the strains were isolated and screened by the dilution plate method, which could efficiently degrade various phenolic acids. The abilities of the strains to degrade phenolic acids were measured by HPLC, and the effects of degrading phenolic acids in soil were verified by a pot experiment. After identification, strain T58 was identified as Burkholderia sp., strain T79 was identified as Burkholderia sp., strain H16 was identified as Pseudomonas sp., and strain T15 was identified as Burkholderia sp. The results showed that, after 21 days of culture, the degradation rates of ferulic acid, p-coumaric acid, vanillin and sinapic acid by strain H16, strain T79, strain T15 and strain T58 were 100%, respectively. Additionally, the degradation rates of gallic acid by the four strains were also 100%. In this study, it was found that the four strains of autotoxin-degrading bacteria had good degradation effects on various phenolic acids, which could not only alleviate the toxic effects of phenolic acids on muskmelon, but also promote the growth of muskmelon seedlings.
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.
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