Effects of grazing intensity on plant community fungal diseases in an alpine grassland.

Fungal pathogens are a vital component of microbial communities and can substantially reduce plant productivity. In grasslands, pathogens and their host plants frequently coexist with large grazing herbivores. However, it remains unclear whether and how grazing alters pathogen transmission and prevalence, particularly when integrating soil and foliar pathogens. Here, we conducted an 8-year field experiment in alpine grasslands on the Qinghai-Tibetan Plateau to examine how soil pathogens and foliar diseases respond to grazing intensity, and to assess the relationship between them. Our results showed that light grazing significantly increased the incidence and severity of plant community foliar diseases, while moderate and heavy grazing significantly reduced them. Similarly, light grazing significantly increased the relative abundance of soil pathogens. Notably, we found a strong positive relationship between soil pathogen abundance and foliar disease occurrence. Mechanistically, light grazing indirectly exacerbated foliar diseases through increases in soil pathogen abundance, whereas moderate and heavy grazing directly suppressed them. Overall, our findings highlight the distinct effects of different grazing intensities on soil pathogens and foliar diseases, and further provide experimental evidence that soil pathogens may play an important role in foliar disease dynamics in grassland ecosystems.