Changes in the Microbial Communities of Picea schrenkiana Needles Following Lirula macrospora Infection

<i>Picea schrenkiana</i> is a keystone species in Central Asian ecosystems currently threatened by climate-driven disease outbreaks. Here, we investigated the causal agent of needle blight and characterized the associated microbial dynamics. By integrating tissue isolation, Koch's postulates, and high-throughput amplicon sequencing across a disease severity level, we confirmed <i>Lirula macrospora</i> as the etiological agent. Community analysis revealed that disease severity is the primary driver of succession, with alpha diversity peaks at the moderate infection stage. Notably, the abundance of <i>Lirula</i> surged from 2.56% in healthy needles to 65.10% in severe cases, displacing the core endophyte <i>Phaeococcomyces</i>, while potentially beneficial bacteria like <i>Sphingomonas</i> showed only transient enrichment. Furthermore, cross-kingdom co-occurrence network analysis revealed marked topological restructuring whereby the system reached a complex ecological "tipping point" during moderate stage before undergoing significant simplification. As the disease progressed, <i>L. macrospora</i> shifted from a peripheral node to a central hub, effectively dismantling the native microbial network. We conclude that <i>L. macrospora</i> infection triggers a cascading collapse of the needle microbiome, driving a phase shift from a healthy homeostasis to a pathogen-dominated state. These findings elucidate the critical mechanisms of pathogen-microbiome interactions and provide a theoretical basis for the ecological management of <i>P. schrenkiana</i> forests.