Broad-scale shift in dominance of arbuscular mycorrhizal trees along the Japanese archipelago associated with tree diseases and climate warming.

Distribution shifts of mycorrhizal tree symbioses are predicted to alter the nutrient cycling in temperate forests worldwide. Yet, our understanding of the drivers and specific impacts of such shifts remains limited. Here, we assign mycorrhizal types to trees at the species and genus level in >13,000 forest plots to assess the dominance of arbuscular mycorrhizal trees based on basal area proportions along the Japanese archipelago in temperate East Asia. We show a significant increase in arbuscular mycorrhizal tree dominance within 15 years associated with climate warming and the spread of tree diseases, contributing to a more important role of arbuscular mycorrhizal symbiosis in forest ecosystems than previously predicted. Arbuscular mycorrhizal tree dominance is negatively related to the ratio of soil carbon and nitrogen stocks, suggesting that tree symbiosis shifts will affect soil nitrogen availability and retention. In light of the global surge of biotic forest disturbance, our results stress the importance of forest pest and disease control to decelerate tree symbiosis shifts and their impact on ecosystem functioning.