To study the effects of dazomet, which is a soil fumigant and microbial inoculant (Trichoderma harzianum) on the bacterial and fungal diversity of continuously cropped strawberry soil, this work aimed to provide a theoretical basis for the treatment of continuously cropped strawberry. The soil of a strawberry greenhouse with continuous cropping for 10 years was used as the research object, and rhizosphere soil samples from strawberry continuous cropping were collected before dazomet fumigation (M0), after dazomet fumigation (M1), after dazomet fumigation in the fruit early phase without the addition of T. harzianum (H0), and after the addition of T. harzianum (H1). The diversity of soil bacteria and fungi was detected via the Illumina HiSeq high-throughput sequencing platform. The results revealed that the richness and diversity of the soil bacterial and fungal communities decreased after dazomet fumigation and that the addition of T. harzianum after dazomet fumigation increased both the richness of the soil bacterial communities and the diversity of the fungal communities. At the genus level, the composition ratios of the soil bacterial and fungal communities in the different treatments also substantially differed. The bacterial community compositions of H0 and H1 were the most similar, while the fungal community compositions of M0 and H0 were the most similar. The analysis of beneficial and harmful dominant genera in the soil revealed that dazomet fumigation could kill pathogenic fungi such as Ilyonectria and Fusarium in the soil and reduce beneficial bacteria and fungi such as Streptomyces, Flavobacterium, Mortierella, and Talaromyces. The addition of T. harzianum to dazomet fumigation can increase the abundance of beneficial bacteria and fungi such as Bacillus, Flavobacterium, and Cladorrhinum in the soil as well as reduce the abundance of pathogenic fungi such as Monilinia, Ilyonectria, and Fusarium. In summary, the use of dazomet fumigation combined with microbial inoculation changed the microbial structure of continuously cropped soil, increased the abundance of beneficial bacteria and fungi, and reduced the abundance of the vast majority of pathogenic fungi in the soil. Therefore, dazomet fumigation combined with microbial inoculation is an effective method for overcoming obstacles to continuous cropping of the strawberry.

To study the effects of different microbial agents on the microbial community structure of continuously cropped strawberry soil after soil fumigation, seven treatments were applied: T1 (Trichoderma harzianum + Bacillus subtilis + actinomycetes), T2 (Trichoderma harzianum + Bacillus subtilis), T3 (Trichoderma harzianum + actinomycetes), T4 (CK) (water control), T5 (Bacillus subtilis), T6 (actinomycetes) and T7 (Trichoderma harzianum). A high-throughput sequencing platform (Illumina HiSeq 2500) was used to analyze the soil bacterial and fungal communities and their compositions. Compared with the T4 (CK) treatment, the application of microbial agents increased the richness and diversity of soil bacteria and fungi, and the effects of single microbial agents and compound microbial agents differed. The richness, diversity indices and population sizes of bacteria and fungi in the T6 treatment were the highest. The Chao1, observed species and Shannon indices of bacteria were 22.51%, 23.56% and 5.61% greater, respectively, than those of T4 (CK). The Chao1, observed species, Shannon and Simpson indices of fungi were 41.28%, 41.83%, 128.02% and 88.65% higher, respectively, than those of T4 (CK). At the genus level, the bacterial community compositions of T2 and T6 were the most similar, and the fungal community compositions of T1 and T5 were the most similar. Analysis of the genera in the dominant communities revealed that the application of microbial agents after dazomet fumigation increased the numbers and recovery rates of soil bacteria and fungi, especially the beneficial fungal genera, Lecanicillium, Cladosporium, Saccharomyces and Aspergillus. An investigation of strawberry growth and yield-related indicators revealed that the T6 treatment resulted in the lowest seedling mortality and the highest yield. In summary, adding microbial agents to soil with continuous cropping of strawberry after fumigation with dazomet is a scientifically sound and effective method for reconstructing the balance of the soil microbial flora and overcoming the obstacles associated with continuous cropping. In this study, the T6 (actinomycetes) treatment presented the best performance.