Tree-microbe mutualisms regulate ecosystem stability in global forests

Forests are the Earth’s largest terrestrial carbon sinks, yet they are increasingly threatened by disturbances such as drought. Identifying the mechanisms that allow forests to resist and recover from disturbance, and thereby maintain ecosystem stability, is essential for predicting biosphere-climate feedbacks. Most tree species form symbioses with either arbuscular mycorrhizal (AM) or ectomycorrhizal (ECM) fungi, and emerging evidence suggests that variation in mycorrhizal association represents a key dimension of plant functional diversity. Despite this, the extent to which these contrasting symbioses shape forest stability, and whether their effects vary across heterogeneous environments, remains unresolved. Here we integrate ground-based observations of forest community composition with satellite-derived vegetation indices from more than 600,000 forest plots worldwide and eddy-covariance gross primary production from 73 forests with carbon dioxide flux towers. We show that, compared with forests dominated by a single mycorrhizal association, forests containing both mycorrhizal associations exhibit greater stability in productivity. These effects were strongest in regions with cold, seasonal, dry, or nutrient-limited conditions and in species-poor forests. This enhanced stability potentially reflects functional complementarity among mycorrhizal associations and the greater drought resistance they confer, rather than faster post-drought recovery. Our findings reveal that diversity in plant-microbe mutualisms—complementing plant taxonomic diversity—constitutes a previously underappreciated dimension for forecasting ecosystem resilience, carbon sequestration, and terrestrial climate feedback.