Shrub encroachment enhances AMF network stability and complexity, while cropland destabilizes AMF communities in a subtropical alpine grassland.

Abstract

Background: Ecosystem conversion, primarily driven by agricultural expansion, has profoundly altered ecosystem structure and function. Grasslands, characterized by deep, nutrient-rich soils that support high soil carbon content, are particularly vulnerable to conversion for agricultural purposes. This transformation significantly impacts soil microbial communities, yet the effects of such changes on the stability and complexity of arbuscular mycorrhizal fungi (AMF) networks remain poorly understood, particularly in subtropical alpine grasslands.

Results: In this study, we investigated how the conversion of natural grasslands into shrublands, artificial woodlands, and croplands affects AMF communities in a subtropical alpine region of China. Our results demonstrate that shrub encroachment increased AMF diversity by up to 25%, and enhanced network modularity and robustness by approximately 20% and 25%, respectively, compared with natural grasslands. This phenomenon may be partially attributed to deep root-mediated niche diversification and the alleviation of soil disturbance in shrubland. In contrast, conversion to cropland decreased AMF diversity by nearly 40%, destabilizing microbial networks due to increased nutrient enrichment and mechanical disturbance. Although the dominant genera Glomus and Paraglomus persisted across all systems, their relative abundance shifted (e.g., a 10-15% reduction of Glomus in croplands). Soil organic carbon, nitrogen, and phosphorus collectively explained up to 89.7% of the variation in AMF network complexity.

Conclusions: These findings address the critical knowledge gap identified in the background regarding AMF responses to land-use changes in subtropical alpine grasslands. By demonstrating that shrub encroachment enhances soil fertility and AMF network stability-contrasting sharply with cropland conversion-our results highlight the importance of preserving natural succession processes to maintain microbial-driven ecosystem functions. This aligns with global efforts to mitigate grassland degradation and supports sustainable management practices in vulnerable alpine regions.