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

## TL;DR

This study shows how infection by Lirula macrospora disrupts the natural microbial balance in Picea schrenkiana needles, leading to a shift from a healthy to a pathogen-dominated state.

## Contribution

The study reveals the cascading collapse of the needle microbiome and the ecological tipping point caused by L. macrospora infection.

## Key findings

- Disease severity is the primary driver of microbial community succession in Picea schrenkiana needles.
- Lirula macrospora becomes a central hub in the microbial network during severe infection, displacing native endophytes.
- The microbial network undergoes significant simplification as the disease progresses.

## Abstract

Picea schrenkiana 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 Lirula macrospora 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 Lirula surged from 2.56% in healthy needles to 65.10% in severe cases, displacing the core endophyte Phaeococcomyces, while potentially beneficial bacteria like Sphingomonas 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, L. macrospora shifted from a peripheral node to a central hub, effectively dismantling the native microbial network. We conclude that L. macrospora 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 P. schrenkiana forests.