Ectomycorrhizal fungi increase phosphorus uptake in Pinus sylvestris var. mongolica and the mechanism controlling Sphaeropsis sapinea

Shoot blight caused by Sphaeropsis sapinea is a major threat to introduced Pinus sylvestris var. mongolica plantations, and effective biocontrol strategies are urgently needed. This study investigated the mechanism by which the ectomycorrhizal fungus (ECMF) Suillus luteus enhances resistance to this disease. We hypothesized that S. luteus inoculation would increase plant phosphorus (P) uptake and modulate the activity of antioxidant enzymes, thereby reducing disease severity. Compared with non-mycorrhizal plants, S. luteus-inoculated S. sapinea-infected seedlings resulted in significant differences in antioxidant enzyme activity and tissue phosphorus content. The mycorrhizal plants also showed lower disease rates and lower disease severity indices. Thus, S. luteus inoculation improves the resistance of P. sylvestris var. mongolica seedlings to shoot blight by activating the antioxidant enzyme system in infected plants and regulating internal phosphorus distribution, thereby reducing seedling senescence and damage from shoot blight. Compared with the control, fungi and plant roots significantly decreased soil pH, and the release of acid phosphatase and organic acids led to a significant (P < 0.05) increase in soil active P content. Moreover, ECMF increased the P content in the roots and leaves of P. sylvestris var. mongolica (P < 0.05). Correlation analysis revealed a significant negative relationship between root P content and disease severity. S. luteus enhances the resistance of P. sylvestris var. mongolica to shoot blight by synergistically improving P acquisition and regulating internal antioxidant defenses. This study provides a new theoretical basis and biological control strategy for the sustainable management of P. sylvestris var. mongolica plantations.