Drought response of trees: differences across mycorrhizal type at the global scale

The association with mycorrhizal fungi, predominantly arbuscular mycorrhizal (AM) fungi or ectomycorrhizal (EM) fungi, is a critical strategy for trees to cope with drought stress, one of the most pervasive stressors affecting forest dynamics. Although experimental evidence suggests varying drought responses among trees with different mycorrhizal associations, a quantitative large‐scale synthesis is still lacking. In this study, we compiled global datasets encompassing three types of drought responses (drought‐induced mortality, growth reduction by severe droughts, and growth recovery from severe droughts) and tested the differences in these drought responses between the two mycorrhizal types using spatial autoregressive models. To elucidate the significant variations in drought responses, we identified key influential climatic factors, edaphic (soil‐related) factors, and species‐specific traits using model selection based on Akaike information criterion. Globally, EM trees experienced slightly greater drought‐induced mortality compared to AM trees but showed significantly less pronounced growth reduction and recovery following severe droughts. The drought responses of EM trees were more strongly influenced by environmental stresses and size‐related traits than those of AM trees, with higher soil pH, greater climate seasonality, and lower plant height significantly increasing the drought responses of EM trees. Despite the above‐mentioned apparent differences, drought responses were generally more drastic at warmer and drier sites for species producing heavier seeds regardless of mycorrhizal type. Our study indicates a potential global vegetation shift favoring AM trees under future climate changes and underscores the critical need to integrate mycorrhizal type considerations into research frameworks for more accurate predictions of forest dynamics in future studies.