Relationship between Bursaphelenchus xylophilus and the diversity of microbial communities in Pinus hwangshanensis

Bursaphelenchus xylophilus, a highly destructive invasive nematode, causes pine wilt disease (PWD) in coniferous trees. This pathogen leads to significant pine mortality and reduced forest productivity, resulting in substantial ecological and economic losses. This research focused on characterizing the internal microbiota of Pinus hwangshanensis, analyzing its organizational patterns, cross-kingdom relationships, and metabolic contributions through comparative analysis between healthy specimens and B. xylophilus infected counterparts. Sampling encompassed multiple tree compartments branches, roots, and trunk segments (upper, middle, lower). Analyses revealed a marked reduction in fungal diversity within infected pines (81% of healthy levels), while bacterial communities showed negligible variation (99% similarity). LEfSe analysis revealed an increased abundance of pathogenic fungi, including Sarea, Cyberlindnera, Mariannaea, Scheffersomyces, Fusarium, Penicillium, and Neocosmospora, in diseased trees, suggested their potential role in exacerbating disease progression through synergistic interactions with nematode or host tissue degradation. Co-occurrence network analysis demonstrated that the bacterial-fungal network in diseased trees was more complex, with a higher proportion of fungal nodes (28.6% vs. 27.8% in healthy trees). Ascomycota and Basidiomycota species emerged as key network hubs, indicating that pathogen invasion strengthened bacterial-fungal associations. Notably, direct bacterial-fungal interactions in diseased trees exhibited a higher proportion of negative correlations (33.2%) compared to healthy trees (22.7%), implying a shift toward antagonistic relationships under pathogen stress. In healthy pines, the predominant functional guilds were animal pathogens (65.87%, primarily in roots), ectomycorrhizal fungi (46.80%, middle trunk), and endophytes (31.27%, middle trunk). The increasing prevalence and diversification of pathogenic threats have progressively weakened the immune resilience of pines. Collectively, our findings suggested B. xylophilus disrupts microbial ecology and collaborates with the resident microbial community to accelerate pine mortality. This study elucidated the impact of B. xylophilus on the microbial community of P. hwangshanensis, particularly its influence on bacterial-fungal ecological associations. By analyzing microbial structural changes from an ecological perspective, this research establishes a theoretical framework to comprehend the pathogenic mechanisms of B. xylophilus from a microbial viewpoint.