Effects of soil pathogenic fungi mediated by litter on the plant seed germination across successional stages of subalpine forests

Soil pathogenic fungi play a critical role in forest succession and biodiversity maintenance. However, how litter decomposition regulates soil pathogenic fungal community structure, and subsequently influences seed germination and survival, remains poorly understood. In this study, we conducted a 360-day laboratory-based litterbag experiment using single-species and mixed-species litter collected from representative plant species across different successional stages in the subalpine forests of western Sichuan, China. The effects of litter decomposition on the community structure of soil total fungi and pathogenic fungi, as well as the mechanisms by which fungal community dynamics affect seed germination and survival, were systematically investigated. Results showed that remaining litter mass was significantly correlated with key physicochemical properties, including total carbon, nitrogen, phosphorus, and lignin content. Litter decomposition significantly altered the community structures of both soil total fungi and pathogenic fungi. Notably, herb litter exhibited a stronger regulatory effect on the pathogenic fungal community than shrub or arbor litter. Specifically, herb litter suppressed seed germination across all successional stages by enhancing the inhibitory effects of pathogenic fungi, whereas shrub and arbor litters influenced germination mainly during mid- to late- successional stages. These findings reveal an ecological pathway through which litter decomposition affects seed germination by regulating soil pathogenic fungal community structure, and clarify the key role of this pathway in plant community assembly during forest succession. This study provides a theoretical basis for further understanding of forest ecosystem restoration mechanisms and biodiversity conservation strategies.