Spatial Differentiation and Community Structure Characteristics of Soil Microorganisms at Variable Hyphosphere Distances in Forest Cultivation Systems of Morchella

Under-forest cultivation of morels is increasingly constrained by soil ecological deterioration, which has become a major obstacle to its sustainable development. This study characterized hyphosphere soil microbiomes of Morchella sextelata M. Kuo under pine canopy at four distances from the fruiting body: 0 cm (R), 20 cm (R20), 40 cm (R40), and uncultivated control (CK). Bacterial and fungal community composition and diversity were analyzed using Illumina NovaSeq high-throughput sequencing. Results showed that the dominant bacterial phyla were Proteobacteria and Acidobacteriota, with RB41, Sphingomonas, and Dongia as the dominant genera. Relative to CK, the abundances of Acidobacteriota and RB41 in R increased by 4.45% and 6.16%, respectively, whereas R20 was enriched in Proteobacteria (+7.77%), Sphingomonas (+0.95%), Dongia, and Bradyrhizobium. For fungi, Ascomycota and Basidiomycota were the dominant phyla, with the principal genera being Sebacina, Microbotryales_gen_Incertae_sedis, and Oidiodendron. Compared with CK, morel cultivation decreased the abundances of Ascomycota and Oidiodendron, with the greatest reductions in R20 (by 8.73% and 3.67%, respectively), while increasing the abundances of Basidiomycota, Sebacina, and Microbotryales_gen_Incertae_sedis, again most markedly in R20, by 17.56%, 14.82%, and 5.74%, respectively. Morel cultivation significantly reduced microbial diversity and evenness (Shannon, Simpson, and Pielou), with the lowest diversity and highest dominance in Zone R. Partial least squares structural equation modeling (PLS-SEM) revealed that soil chemical properties and enzyme activities negatively drove dominant bacterial genera but positively drove dominant fungal genera. Overall, under-forest cultivation of M. sextelata significantly reduced hyphosphere microbial diversity and reshaped microbial community structure in a distance-dependent manner: Zone R was dominated by Acidobacteriota; Zone R20 was enriched with nitrogen-cycling beneficial bacteria (Dongia, Sphingomonas, and Bradyrhizobium) and beneficial fungi (Sebacina and Microbotryales_gen_Incertae_sedis); Zone R40 exhibited relatively optimal fungal diversity.