Shrubs inhibit plant diseases by intercepting light in alpine meadows

Abstract Climate change is disproportionately impacting mountain ecosystems, leading to widespread shrub expansion into alpine meadows. Shrub encroachment alters the albedo, carbon budget and warming rate in alpine grasslands, but it remains challenging to predict how shrub encroachment will affect biological interactions, including plant–pathogen interactions. Here, we established a field experiment with four shrub treatments (i.e. shrub encroachment, artificial shrub addition, shrub removal and a natural grassland). Using two treatment combinations with distinct controls, we evaluated shrub effects on pathogen infection in herbaceous plants and examined the underlying regulatory pathways through local herbaceous plant community, microclimate and soils. Shrub encroachment inhibited foliar fungal diseases, especially those caused by necrotrophic pathogens (mainly leaf spot), and these effects primarily derived from reducing light penetration through shrub canopies. Following shrub removal, herbaceous above‐ground biomass rebounded, which in turn increased foliar disease pressure. Overall, this study highlights the profound effects of shrub encroachment on alpine grassland ecosystems, underscoring the necessity of considering its complex role in plant‐pathogen interactions. These findings have important implications for sustaining grassland biodiversity and productivity and for assessing the ecological outcomes of shrub‐removal management in mountain ecosystems. Read the free Plain Language Summary for this article on the Journal blog.